Separation method, display device, display module, and electronic device

ABSTRACT

The yield of a separation process is improved. The mass productivity of a display device which is formed through a separation process is improved. A layer is formed over a substrate with use of a material including a resin or a resin precursor. Next, a resin layer is formed by performing heat treatment on the layer. Next, a layer to be separated is formed over the resin layer. Then, the layer to be separated and the substrate are separated from each other. The heat treatment is performed in an atmosphere containing oxygen or while supplying a gas containing oxygen.

TECHNICAL FIELD

One embodiment of the present invention relates to a separation method,a display device, a display module, an electronic device, and amanufacturing method of a display device.

Note that one embodiment of the present invention is not limited to theabove technical field. Examples of the technical field of one embodimentof the present invention include a semiconductor device, a displaydevice, a light-emitting device, a power storage device, a memorydevice, an electronic device, a lighting device, an input device (suchas a touch sensor), an input/output device (such as a touch panel), amethod for driving any of them, and a method for manufacturing any ofthem.

In this specification and the like, a semiconductor device generallymeans a device that can function by utilizing semiconductorcharacteristics. A transistor, a semiconductor circuit, an arithmeticdevice, a memory device, and the like are each an embodiment of thesemiconductor device. In addition, an imaging device, an electro-opticaldevice, a power generation device (e.g., a thin film solar cell and anorganic thin film solar cell), and an electronic device each may includea semiconductor device.

BACKGROUND ART

Display devices using organic electroluminescent (EL) elements or liquidcrystal elements have been known. Examples of the display device alsoinclude a light-emitting device provided with a light-emitting elementsuch as a light-emitting diode (LED), and electronic paper performingdisplay with an electrophoretic method or the like.

The organic EL element generally has a structure in which a layercontaining a light-emitting organic compound is provided between a pairof electrodes. By voltage application to this element, thelight-emitting organic compound can emit light. A display deviceincluding such an organic EL element can be thin and lightweight andhave high contrast and low power consumption.

Further, by forming a semiconductor element such as a transistor and adisplay element such as the organic EL element over a flexible substrate(film), a flexible display device can be provided.

Patent Document 1 discloses a method for manufacturing a flexibledisplay device by separating a heat-resistant resin layer from asupporting substrate (a glass substrate) after the glass substrateprovided with a heat-resistant resin layer and electronic elements isirradiated with laser light through a sacrificial layer.

REFERENCE Patent Document [Patent Document 1] Japanese Published PatentApplication No. 2015-223823 DISCLOSURE OF INVENTION

An object of one embodiment of the present invention is to provide anovel separation method or a novel manufacturing method of a displaydevice. An object of one embodiment of the present invention is toprovide a separation method or a manufacturing method of a displaydevice at low cost with high mass productivity. An object of oneembodiment of the present invention is to provide a separation methodwith a high yield. An object of one embodiment of the present inventionis to perform separation using a large-sized substrate. An object of oneembodiment of the present invention is to manufacture a display deviceusing a large-sized substrate. An object of one embodiment of thepresent invention is to provide a manufacturing method of a displaydevice with a simplified manufacturing process. An object of oneembodiment of the present invention is to manufacture a display deviceat low temperatures.

Another object of one embodiment of the present invention is to providea display device with low power consumption. Another object of oneembodiment of the present invention is to provide a display device withhigh visibility regardless of the ambient brightness. Another object ofone embodiment of the present invention is to provide an all-weatherdisplay device. Another object of one embodiment of the presentinvention is to provide a display device with high convenience. Anotherobject of one embodiment of the present invention is to provide adisplay device with high reliability. Another object of one embodimentof the present invention is to reduce the thickness or weight of adisplay device. Another object of one embodiment of the presentinvention is to provide a display device having flexibility or a curvedsurface. Another object of one embodiment of the present invention is toprovide a robust display device. Another object of one embodiment of thepresent invention is to provide a novel display device, a novelinput/output device, a novel electronic device, or the like.

Note that the descriptions of these objects do not disturb the existenceof other objects. One embodiment of the present invention does notnecessarily achieve all the objects. Further, it is a problem that apolarizing plate having a high polarization degree is expensive.

One embodiment of the present invention is a separation method includingthe steps of forming a first layer over a substrate with use of amaterial containing a resin or a resin precursor; performing a firstheat treatment on the first layer while supplying a gas containingoxygen to form a first resin layer; forming a layer to be separated overthe first resin layer; and separating the layer and the substrate fromeach other.

One embodiment of the present invention is a separation method includingthe steps of forming a first layer over a substrate with use of amaterial containing a resin or a resin precursor, performing a firstheat treatment on the first layer while supplying a gas containingoxygen to form a first resin layer; forming an insulating layer coveringan end portion of the first resin layer over the substrate and the firstresin layer; forming a transistor containing a metal oxide in a channelformation region over the first resin layer with the insulating layerpositioned therebetween; separating at least part of the first resinlayer from the substrate to form a separation starting point; andseparating the transistor and the substrate from each other.

One embodiment of the present invention is a separation method includingthe steps of forming a first layer over a substrate with use of amaterial containing a resin or a resin precursor; performing a firstheat treatment on the first layer in an atmosphere containing oxygen toform a first resin layer; forming a second layer covering an end portionof the first resin layer over the substrate and the first resin layer;performing a second heat treatment on the second layer in an atmospherecontaining less oxygen than the atmosphere of the first treatment toform a second resin layer covering an end portion of the first resinlayer; forming a transistor including a metal oxide in a channelformation region over the first resin layer with the second resin layerpositioned therebetween; separating at least part of the first resinlayer from the substrate to form a separation starting point; andseparating the transistor and the substrate from each other.

One embodiment of the present invention is a separation method includingthe steps of forming a first layer over a substrate with use of amaterial containing a resin or a resin precursor; performing a firstheat treatment on the first layer while supplying a gas containingoxygen to form a first resin layer; forming a second layer covering anend portion of the first resin layer over the substrate and the firstresin layer; performing a second heat treatment on the second layerwithout supplying a gas containing oxygen or while supplying a gas whoseproportion of oxygen is lower than a proportion of a gas used in thefirst heat treatment; forming a transistor including a metal oxide in achannel formation region over the first resin layer with the secondresin layer positioned therebetween; separating at least part of thefirst resin layer from the substrate to form a separation startingpoint; and separating the transistor and the substrate from each other.

The second heat treatment may be performed while supplying a nitrogengas.

The second heat treatment may be performed at a temperature lower thanthe temperature of the first heat treatment while supplying a mixed gascontaining nitrogen and oxygen.

In the case where the temperature of the second heat treatment is lowerthan the temperature of the first heat treatment, the proportion ofoxygen in the gas used in the first heat treatment may be equal to theproportion of oxygen in the gas used in the second heat treatment.

The first heat treatment may be performed while supplying a mixed gas inwhich the proportion of an oxygen gas flow rate in a whole gas flow rateis greater than or equal to 5% and less than or equal to 50%.

The first heat treatment may be performed at a temperature of greaterthan or equal to 350° C. and less than or equal to 450° C. whilesupplying a mixed gas containing nitrogen and oxygen.

The first resin layer may be formed to a thickness greater than or equalto 1 μm and less than or equal to 3 μm.

The first layer may be formed with use of a solution with a viscosity ofgreater than or equal to 5 cP and less than 100 cP.

The first layer may be formed using a spin coater.

It is preferable that the transistor be manufactured at a temperaturelower than or equal to the temperature of the first heat treatment.

The first layer may be formed using a photosensitive resin.

One embodiment of the present invention is a display device including afirst resin layer, a second resin layer over the first resin layer, atransistor over the second resin layer, and a display elementelectrically connected to the transistor. The oxygen concentrationmeasured by X-ray photoelectron spectroscopy (XPS) analysis performed ona surface of the first resin layer that is opposite to a surface on thesecond resin layer side is higher than or equal to 10 atomic %. Thefirst resin layer preferably has a thickness greater than or equal to 1μm and less than or equal to 3 μm. The transistor preferably includesmetal oxide in a channel formation region.

One embodiment of the present invention is a display module includingany of the above display devices and a circuit board such as a flexibleprinted circuit (FPC).

One embodiment of the present invention is an electronic deviceincluding the above display module and at least one of an antenna, abattery, a housing, a camera, a speaker, a microphone, and an operationbutton.

One embodiment of the present invention can provide a novel separationmethod or a novel manufacturing method of a display device. Oneembodiment of the present invention can provide a separation method or amanufacturing method of a display device at low cost with high massproductivity. One embodiment of the present invention can provide aseparation method with a high yield. One embodiment of the presentinvention can perform separation using a large-sized substrate. Oneembodiment of the present invention can manufacture a display deviceusing a large-sized substrate. One embodiment of the present inventioncan provide a manufacturing method of a display device with a simplifiedmanufacturing process. One embodiment of the present invention canmanufacture a display device at low temperatures.

One embodiment of the present invention can provide a display devicewith low power consumption. One embodiment of the present invention canprovide a display device with high visibility regardless of the ambientbrightness. One embodiment of the present invention can provide anall-weather display device. One embodiment of the present invention canprovide a display device with high convenience. One embodiment of thepresent invention can provide a display device with high reliability.One embodiment of the present invention can reduce the thickness orweight of a display device. One embodiment of the present invention canprovide a display device with flexibility or having a curved surface.One embodiment of the present invention can provide a display devicethat is unlikely to be broken. One embodiment of the present inventioncan provide a novel display device, a novel input/output device, a novelelectronic device, or the like.

Note that the description of these effects does not preclude theexistence of other effects. One embodiment of the present invention doesnot necessarily have all the effects listed above. Other effects can bederived from the description of the specification, the drawings, theclaims, and the like.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A to 1E are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 2A to 2C are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 3A to 3C are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 4A, 4B, 4C, 4D1, 4D2, and 4E are cross-sectional viewsillustrating an example of a manufacturing method of a display device.

FIGS. 5A, 5B1, and 5B2 are cross-sectional views and a top viewillustrating an example of a manufacturing method of a display device.

FIGS. 6A and 6B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 7A to 7C are a top view and cross-sectional views illustrating anexample of a display device.

FIGS. 8A and 8B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 9A to 9C are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 10A to 10C are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 11A to 11C are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 12A and 12B are a cross-sectional view and a top view illustratingan example of a manufacturing method of a display device.

FIGS. 13A and 13B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 14A and 14B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 15A and 15B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 16A and 16B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 17A to 17E are a cross-sectional view and top views illustratingan example of a manufacturing method of a display device.

FIGS. 18A and 18B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 19A and 19B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 20A and 20B are a top view and a cross-sectional view illustratingan example of a display device.

FIGS. 21A to 21E are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 22A1, 22A2, and 22B are cross-sectional views and a top viewillustrating an example of a manufacturing method of a display device.

FIG. 23 is a perspective view illustrating an example of a displaydevice.

FIG. 24 is a cross-sectional view illustrating an example of a displaydevice.

FIG. 25 is a cross-sectional view illustrating an example of a displaydevice.

FIG. 26 is a cross-sectional view illustrating an example of a displaydevice.

FIGS. 27A to 27F are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 28A to 28C are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 29A and 29B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 30A and 30B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 31A to 31D are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 32A and 32B are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIGS. 33A to 33C are cross-sectional views illustrating an example of amanufacturing method of a display device.

FIG. 34A illustrates an example of a display device, and FIGS. 34B1,34B2, 34B3, and 34B4 each illustrate an example of a pixel.

FIG. 35 is a circuit diagram illustrating an example of a pixel circuitin a display device.

FIG. 36A is a circuit diagram illustrating an example of a pixel circuitof a display device, and FIG. 36B illustrates an example of a pixel.

FIG. 37 illustrates an example of a display module.

FIGS. 38A to 38D illustrate examples of electronic devices.

FIGS. 39A to 39E illustrate examples of electronic devices.

FIGS. 40A and 40B are external photographs showing the separationresults of Example 1.

FIG. 41 is a photograph showing the appearances of separation results ofExample 1.

FIGS. 42A1, 42A2, 42B, 42C1, 42C2, and 42D are cross-sectional views andtop views illustrating a separation method in Example 2.

FIG. 43 is photographs showing the appearances of separation results ofExample 2.

FIG. 44A is a perspective view illustrating a device which is used formeasurement of force required for separation in Example 2 and FIG. 44Bis a cross-sectional view illustrating a sample in Example 2.

FIG. 45 shows measurement results of force required for separation inExample 2.

FIGS. 46A to 46C are each a cross-sectional STEM image of a sample 2A inExample 2.

FIGS. 47A to 47C are each a cross-sectional STEM image of a sample 2C inExample 2.

FIGS. 48A to 48C are each a cross-sectional STEM image of a sample 2E inExample 2.

FIGS. 49A and 49B show XPS analysis results of samples in Example 4.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments will be described in detail with reference to drawings. Notethat the present invention is not limited to the following description.It will be readily appreciated by those skilled in the art that modesand details of the present invention can be modified in various wayswithout departing from the spirit and scope of the present invention.Thus, the present invention should not be construed as being limited tothe description in the following embodiments.

Note that in structures of the present invention described below, thesame portions or portions having similar functions are denoted by thesame reference numerals in different drawings, and a description thereofis not repeated. Further, the same hatching pattern is applied toportions having similar functions, and the portions are not especiallydenoted by reference numerals in some cases.

The position, size, range, or the like of each structure illustrated indrawings is not accurately represented in some cases for easyunderstanding. Therefore, the disclosed invention is not necessarilylimited to the position, size, range, or the like disclosed in thedrawings.

Note that the terms “film” and “layer” can be interchanged with eachother depending on the case or circumstances. For example, the term“conductive layer” can be changed into the term “conductive film”. Also,the term “insulating film” can be changed into the term “insulatinglayer”.

Note that in this specification and the like, a “substrate” preferablyhas a function of supporting at least one of a functional circuit, afunctional element, a functional film, and the like. A “substrate” doesnot necessary have a function of supporting a functional circuit, afunctional element, a functional film, and the like, and may have afunction of protecting a surface of the device, or a function of sealingat least one of a functional circuit, a functional element, a functionalfilm, and the like, for example.

In this specification and the like, a metal oxide means an oxide ofmetal in a broad sense. Metal oxides are classified into an oxideinsulator, an oxide conductor (including a transparent oxide conductor),an oxide semiconductor (also simply referred to as an OS), and the like.For example, a metal oxide used in a semiconductor layer of a transistoris called an oxide semiconductor in some cases. In other words, an OSFET is a transistor including a metal oxide or an oxide semiconductor.

In this specification and the like, a metal oxide including nitrogen isalso called a metal oxide in some cases. Moreover, a metal oxideincluding nitrogen may be called a metal oxynitride.

In this specification and the like, “c-axis aligned crystal (CAAC)” or“cloud-aligned composite (CAC)” might be stated. CAAC refers to anexample of a crystal structure, and CAC refers to an example of afunction or a material composition.

An example of a crystal structure of an oxide semiconductor or a metaloxide is described. Note that an oxide semiconductor deposited by asputtering method using an In—Ga—Zn oxide target (In:Ga:Zn=4:2:4.1 in anatomic ratio) is described below as an example. An oxide semiconductorformed by a sputtering method using the above-mentioned target at asubstrate temperature of higher than or equal to 100° C. and lower thanor equal to 130° C. is referred to as sIGZO, and an oxide semiconductorformed by a sputtering method using the above-mentioned target with thesubstrate temperature set at room temperature (R.T.) is referred to astIGZO. For example, sIGZO has one or both crystal structures of nanocrystal (nc) and CAAC. Furthermore, tIGZO has a crystal structure of nc.Note that room temperature (R.T.) herein also refers to a temperature ofthe time when a substrate is not heated intentionally.

In this specification and the like, CAC-OS or CAC-metal oxide has afunction of a conductor in a part of the material and has a function ofa dielectric (or insulator) in another part of the material; as a whole,CAC-OS or CAC-metal oxide has a function of a semiconductor. In the casewhere CAC-OS or CAC-metal oxide is used in a semiconductor layer of atransistor, the conductor has a function of letting electrons (or holes)serving as carriers flow, and the dielectric has a function of notletting electrons serving as carriers flow. By the complementary actionof the function as a conductor and the function as a dielectric, CAC-OSor CAC-metal oxide can have a switching function (on/off function). Inthe CAC-OS or CAC-metal oxide, separation of the functions can maximizeeach function.

In this specification and the like, CAC-OS or CAC-metal oxide includesconductor regions and dielectric regions. The conductor regions have theabove-described function of the conductor, and the dielectric regionshave the above-described function of the dielectric. In some cases, theconductor regions and the dielectric regions in the material areseparated at the nanoparticle level. In some cases, the conductorregions and the dielectric regions are unevenly distributed in thematerial. When observed, the conductor regions are coupled in acloud-like manner with their boundaries blurred, in some cases.

In other words, CAC-OS or CAC-metal oxide can be called a matrixcomposite or a metal matrix composite.

Furthermore, in the CAC-OS or CAC-metal oxide, the conductor regions andthe dielectric regions each have a size of more than or equal to 0.5 nmand less than or equal to 10 nm, preferably more than or equal to 0.5 nmand less than or equal to 3 nm and are dispersed in the material, insome cases.

Embodiment 1

In this embodiment, a separation method of one embodiment of the presentinvention and a manufacturing method of a display device of oneembodiment of the present invention will be described with reference toFIGS. 1A to 1E, FIGS. 2A to 2C, FIGS. 3A to 3C, FIGS. 4A, 4B, 4C, 4D1,4D2, and 4E, FIGS. 5A, 5B1, and 5B2, FIGS. 6A and 6B, FIGS. 7A to 7C,FIGS. 8A and 8B, FIGS. 9A to 9C, FIGS. 10A to 10C, FIGS. 11A to 11C,FIGS. 12A and 12B, FIGS. 13A and 13B, FIGS. 14A and 14B, FIGS. 15A and15B, FIGS. 16A and 16B, FIGS. 17A to 17E, FIGS. 18A and 18B, FIGS. 19Aand 19B, and FIGS. 20A and 20B.

In this embodiment, a display device that includes a transistor and anorganic EL element (also referred to as an active matrix organic ELdisplay device) will be described as an example. The display device canhave flexibility by using a flexible material for a substrate. Note thatone embodiment of the present invention is not limited to alight-emitting device, a display device, and an input/output device(e.g., a touch panel) that include organic EL elements, and oneembodiment of the present invention can be applied to a variety ofdevices such as a semiconductor device, a light-emitting device, adisplay device, and an input/output device that include other kinds offunctional elements.

In the separation method of one embodiment of the present invention,first, a material including a resin or a resin precursor is formed as afirst layer over the substrate. Then, first heat treatment is performedon the first layer, whereby a first resin layer is formed. Then, a layerto be separated is formed over the first resin layer. Then, the layer tobe separated and the substrate are separated from each other. The firstheat treatment is performed in an atmosphere containing oxygen. Thefirst heat treatment is preferably performed while supplying a gascontaining oxygen.

The first resin layer formed by heating the first layer in an atmospherecontaining enough oxygen includes a large amount of oxygen and thus canbe easily separated from the substrate.

In the separation method of one embodiment of the present invention, thefirst resin layer can be easily separated from the substrate bycontrolling heat conditions used to form the first resin layer. That is,a step of irradiating an entire surface of the first resin layer withlaser light to increase the separability of the first resin layer is notnecessary.

If the entire surface of the first resin layer is irradiated with laserlight, use of a linear laser beam is suitable, but a laser apparatus forthe linear laser beam irradiation is expensive and requires high runningcosts. In the separation method of one embodiment of the presentinvention, the laser apparatus is not necessary, leading to significantcost savings. Moreover, the separation method is easily applicable to alarge-sized substrate.

Because the step of irradiating the entire surface of the first resinlayer with laser light through the substrate is not performed, thesubstrate can be prevented from being damaged by the laser lightirradiation. The substrate after being used once is less likely todecrease in strength; thus, the substrate can be reused, leading to costsavings.

In another separation method of one embodiment of the present invention,first, a material including a resin or a resin precursor is formed as afirst layer over a substrate. Then, first heat treatment is performed onthe first layer, whereby a first resin layer is formed. Then, aninsulating layer covering an end portion of the first resin layer isformed over the substrate and the first resin layer. Then, a transistorincluding metal oxide in a channel formation region is formed over thefirst resin layer with the insulating layer positioned between the firstresin layer and the transistor. Then, a separation starting point isformed by separating at least part of the first resin layer from thesubstrate. Then, the transistor and the substrate are separated fromeach other. The first heat treatment is performed in an atmospherecontaining oxygen. The first heat treatment is preferably performedwhile supplying a gas containing oxygen.

A portion that is in contact with the first resin layer and a portionthat is in contact with the insulating layer are provided for thesubstrate. The insulating layer is formed covering the end portion ofthe first resin layer. The adhesion of the insulating layer to thesubstrate is stronger than the adhesion of the first resin layer to thesubstrate. By the formation of the insulating layer covering the endportion of the first resin layer, unintentional separation of the firstresin layer from the substrate can be inhibited even in the case wherethe first resin layer has high separability. For example, separation ofthe first resin layer that will occur at the time of transferring thesubstrate can be inhibited. Furthermore, the separation starting pointenables separation of the substrate and the first resin layer from eachother at a desired time. That is, in the separation method of thisembodiment, the time at which the separation occurs can be controlledand high separability can be achieved. This can improve the yield of theseparation process and the manufacturing process of the display device.

In another separation method of one embodiment of the present invention,first, a material including a resin or a resin precursor is formed as afirst layer over a substrate. Then, first heat treatment is performed onthe first layer in an atmosphere containing oxygen, whereby a firstresin layer is formed. Then, a second layer covering an end portion ofthe first resin layer is formed over the substrate and the first resinlayer. Then, second heat treatment is performed on the second layer inan atmosphere containing less oxygen than the atmosphere of the firstheat treatment, whereby a second resin layer covering the end portion ofthe first resin layer is formed. Then, a transistor including metaloxide in a channel formation region is formed over the first resin layerwith the second resin layer positioned between the first resin layer andthe transistor. Then, a separation starting point is formed byseparating at least part of the first resin layer from the substrate.Then, the transistor and the substrate are separated from each other.

The first heat treatment is performed in an atmosphere containingoxygen. The first heat treatment is preferably performed while supplyinga gas containing oxygen.

The second heat treatment is preferably performed in an atmospherecontaining less oxygen than the atmosphere of the first heat treatment.The second heat treatment is preferably performed without supplying agas containing oxygen or while supplying a gas whose proportion ofoxygen is lower than that of a gas used in the first heat treatment.

The separability of the second resin layer is lower than theseparability of the first resin layer because the second resin layer isformed by heating in the atmosphere containing less oxygen than theatmosphere of the first heat treatment.

Note that in some cases, it can be confirmed that the amount of oxygencontained in the first resin layer is larger than the amount of oxygencontained in the second resin layer through analysis of the oxygenamount or oxygen concentration in the film or of the film surface.Specifically, analysis using secondary ion mass spectrometry (SIMS),XPS, or the like can be used.

A portion that is in contact with the first resin layer and a portionthat is in contact with the second resin layer are provided for thesubstrate. The second resin layer is formed covering the end portion ofthe first resin layer. The adhesion of the second resin layer to thesubstrate is stronger than the adhesion of the first resin layer to thesubstrate. By the formation of the second resin layer covering the endportion of the first resin layer, separation of the first resin layerfrom the substrate that will occur at an unintended time can beinhibited even in the case where the first resin layer has highseparability. Furthermore, the separation starting point enablesseparation of the substrate and the first resin layer from each other ata desired time. That is, in the separation method of this embodiment,the time at which the separation occurs can be controlled and highseparability can be achieved. This can improve the yield of theseparation process and the manufacturing process of the display device.

Note that even when the atmosphere of the first heat treatment is thesame as the atmosphere of the second heat treatment, the separability ofthe first resin layer can be made different from the separability of thesecond resin layer in some cases by setting the temperature of thesecond heat treatment sufficiently lower than the temperature of thefirst heat treatment.

The first layer and the second layer may be formed using aphotosensitive material. With the photosensitive material, a resin layerwith a desired shape can be easily formed.

The display device of this embodiment preferably includes metal oxide inthe channel formation region of the transistor. The metal oxide canserve as an oxide semiconductor.

In the case where low temperature polysilicon (LTPS) is used for thechannel formation region of the transistor, the first resin layer andthe second resin layer are required to have heat resistance because heatat a temperature of approximately 500° C. to 550° C. needs to beapplied. Furthermore, the first resin layer and the second resin layerneed to have a large thickness so that damage in a step of lasercrystallization is reduced.

In contrast, the transistor including the metal oxide in the channelformation region can be formed at a temperature lower than or equal to350° C., or even lower than or equal to 300° C. Thus, the first resinlayer and the second resin layer are not required to have high heatresistance. Accordingly, the heat resistant temperature of the firstresin layer and the second resin layer can be low, and the range ofchoices for the materials can be widened. Furthermore, the transistorincluding metal oxide in the channel formation region does not need alaser crystallization step; thus, the first resin layer and the secondresin layer can be thin. Since first resin layer and the second resinlayer are not required to have high heat resistance and can be thinned,the manufacturing costs of a device can be significantly reduced. Metaloxide is preferably used, in which case the steps can be simplified ascompared with the case where LTPS is used.

The first resin layer and the second resin layer may each have athickness greater than or equal to 0.1 μm and less than or equal to 3μm. By forming the first resin layer and the second resin layer thin,the display device can be manufactured at low cost. The display devicecan be light-weight and thin. The display device can have higherflexibility.

In this embodiment, the transistor or the like is formed at atemperature lower than or equal to the heat resistance temperature ofthe first resin layer and lower than or equal to the heat resistancetemperature of the second resin layer. The heat resistance of the resinlayer can be measured by, for example, a weight loss percentage due toheat, specifically, the 5% weight loss temperature. In the separationmethod and the manufacturing method of the display device of thisembodiment, the maximum process temperature can be low. For example, the5% weight loss temperature of the first resin layer and the 5% weightloss temperature of the second resin layer can each be higher than orequal to 200° C. and lower than or equal to 550° C., higher than orequal to 200° C. and lower than or equal to 450° C., higher than orequal to 200° C. and lower than or equal to 400° C., or higher than orequal to 200° C. and lower than or equal to 350° C. Thus, the range ofchoices for the material is widened. Note that the 5% weight losstemperature of the first resin layer or the second resin layer may behigher than 550° C.

The manufacturing method of the display device of this embodiment willbe specifically described below.

Note that the thin films included in the display device (i.e., theinsulating film, the semiconductor film, the conductive film, and thelike) can be formed by any of a sputtering method, a chemical vapordeposition (CVD) method, a vacuum evaporation method, a pulsed laserdeposition (PLD) method, an atomic layer deposition (ALD) method, andthe like. As the CVD method, a plasma-enhanced chemical vapor deposition(PECVD) method or a thermal CVD method may be used. As an example of thethermal CVD method, a metal organic chemical vapor deposition (MOCVD)method may be used.

Alternatively, the thin films constituting the display device (i.e., theinsulating film, the semiconductor film, the conductive film, and thelike) can be formed by a method such as spin coating, dipping, spraycoating, inkjet printing, dispensing, screen printing, or offsetprinting, or with a doctor knife, a slit coater, a roll coater, acurtain coater, or a knife coater.

When thin films included in the display device are processed, alithography method or the like can be used for the processing.Alternatively, island-shaped thin films may be formed by a filmformation method using a blocking mask. Alternatively, the thin filmsmay be processed by a nano-imprinting method, a sandblasting method, alift-off method, or the like. As the photolithography method, there area method in which a resist mask is formed over a thin film to beprocessed, the thin film is processed by etching or the like, and theresist mask is removed and a method in which a photosensitive thin filmis formed, and the photosensitive thin film is exposed to light anddeveloped to be processed in a desirable shape.

In the case of using light in the lithography method, any of an i-line(light with a wavelength of 365 nm), a g-line (light with a wavelengthof 436 nm), and an h-line (light with a wavelength of 405 nm), orcombined light of any of them can be used for exposure. Alternatively,ultraviolet light, KrF laser light, ArF laser light, or the like can beused. Exposure may be performed by liquid immersion exposure technique.As the light for the exposure, extreme ultra-violet light (EUV) orX-rays may be used. Instead of the light for the exposure, an electronbeam can be used. It is preferable to use EUV, X-rays, or an electronbeam because extremely minute processing can be performed. Note that inthe case of performing exposure by scanning of a beam such as anelectron beam, a photomask is not needed.

For etching of the thin film, dry etching, wet etching, a sandblastmethod, or the like can be used.

Manufacturing Method Example 1

First, a first layer 24 a is formed over a formation substrate 14 (FIG.1A).

In FIG. 1A, an example of forming the first layer 24 a over an entiresurface of the formation substrate 14 by a coating method is shown. Theformation method is not limited to a coating method, and the first layer24 a may be formed over the formation substrate 14 by a printing methodor the like. The first layer 24 a that has an island-like shape, thefirst layer 24 a that has an opening or an uneven shape, or the like maybe formed over the formation substrate 14.

The first layer 24 a can be formed using any of a variety of resinmaterials (including a resin precursor).

The first layer 24 a is preferably formed using a thermosettingmaterial.

The first layer 24 a may be formed using a material havingphotosensitivity or a material that does not have photosensitivity (alsoreferred to as a non-photosensitive material).

In the case where a photosensitive material is used for the first layer24 a, part of the first layer 24 a can be removed by a lithographymethod using light, whereby the first resin layer 23 a with a desiredshape can be formed.

The first layer 24 a is preferably formed using a material containing apolyimide resin or a polyimide resin precursor. The first layer 24 a canbe formed using, for example, a material containing a polyimide resinand a solvent or a material containing polyamic acid and a solvent. Apolyimide is a material that is suitably used for formation of aplanarization film or the like of a display device, and therefore, thefilm formation apparatus and the material can be shared. Thus, there isno need to prepare another apparatus and another material to obtain thestructure of one embodiment of the present invention.

Examples of resin materials which can be used to form the first resinlayer 24 a include an acrylic resin, an epoxy resin, a polyamide resin,a polyimide-amide resin, a siloxane resin, a benzocyclobutene-basedresin, and a phenol resin, a precursor of any of the resins, and thelike.

The first layer 24 a is preferably formed with a spin coater. The spincoating method enables formation of a uniform thin film over a largesubstrate.

The first layer 24 a is preferably formed using a solution having aviscosity of greater than or equal to 5 cP and less than 500 cP, furtherpreferably greater than or equal to 5 cP and less than 100 cP, stillfurther preferably greater than or equal to 10 cP and less than or equalto 50 cP. The lower the viscosity of the solution is, the easier thecoating is. Furthermore, the lower the viscosity of the solution is, themore the entry of bubbles can be prevented, leading to a film with goodquality.

Alternatively, the first layer 24 a can be formed by dipping, spraycoating, ink-jetting, dispensing, screen printing, or offset printing,or with a doctor knife, a slit coater, a roll coater, a curtain coater,or a knife coater, for example.

The formation substrate 14 has stiffness high enough for easy transferand has resistance to heat applied in the manufacturing process.Examples of a material that can be used for the formation substrate 14include glass, quartz, ceramics, sapphire, a resin, a semiconductor, ametal, and an alloy. Examples of the glass include alkali-free glass,barium borosilicate glass, and aluminoborosilicate glass.

Then, first heat treatment is performed on the first layer 24 a, wherebythe first resin layer 23 a is formed (FIG. 1B).

The first heat treatment is performed in an atmosphere containingoxygen.

The larger the amount of oxygen contained in the first resin layer 23 ais, the smaller the force required for separation of the first resinlayer 23 a can be. The higher the proportion of oxygen in the atmosphereof the first heat treatment is, the larger the amount of oxygencontained in the first resin layer 23 a can be, so that the separabilityof the first resin layer 23 a can be increased.

The first heat treatment can be performed using an atmosphere containingoxygen in a chamber of a heating apparatus, for example. Alternatively,the first heat treatment can be performed with a hot plate or the likein an air atmosphere.

The partial pressure of oxygen in the atmosphere at the time ofperforming the first heat treatment is preferably higher than or equalto 5% and lower than 100%, further preferably higher than or equal to10% and lower than 100%, still further preferably higher than or equalto 15% and lower than 100%.

The first heat treatment is preferably performed while supplying a gascontaining oxygen into the chamber of the heating apparatus. Forexample, the first heat treatment is preferably performed whilesupplying only an oxygen gas or a mixed gas containing an oxygen gas.Specifically, a mixed gas containing oxygen and nitrogen or a rare gas(such as argon) can be used.

Some heat apparatuses deteriorate in the case where the proportion ofoxygen in the atmosphere is high. Therefore, in the case where a mixedgas containing an oxygen gas is used, the proportion of the flow rate ofthe oxygen gas in the flow rate of the whole mixed gas is preferably sethigher than or equal to 5% and lower than or equal to 50%, furtherpreferably higher than or equal to 10% and lower than or equal to 50%,still further preferably higher than or equal to 15% and lower than orequal to 50%.

The temperature of the first heat treatment is preferably higher than orequal to 200° C. and lower than or equal to 500° C., further preferablyhigher than or equal to 250° C. and lower than or equal to 475° C.,still further preferably higher than or equal to 300° C. and lower thanor equal to 450° C.

The higher the temperature of the first heat treatment is, the higherthe separability of the first resin layer 23 a can be.

By the first heat treatment, released gas components (e.g., hydrogen orwater) in the first resin layer 23 a can be reduced. In particular,heating is preferably performed at a temperature higher than or equal tothe formation temperature of each layer formed over the first resinlayer 23 a. Thus, a gas released from the first resin layer 23 a in themanufacturing process of the transistor can be significantly reduced.

For example, in the case where the manufacturing temperature of thetransistor is below 350° C., a film to be the first resin layer 23 a ispreferably heated at a temperature higher than or equal to 350° C. andlower than or equal to 450° C., further preferably higher than or equalto 350° C. and lower than or equal to 400° C., still further preferablyhigher than or equal to 350° C. and lower than or equal to 375° C. Thus,a gas released from the first resin layer 23 a in the manufacturingprocess of the transistor can be significantly reduced.

The maximum temperature in manufacturing the transistor is preferablyequal to the temperature of the first heat treatment, in which case themaximum temperature in manufacturing the display device can be preventedfrom being increased by the first heat treatment.

The longer the heating time of the first heat treatment is, the higherthe separability of the first resin layer 23 a can be.

By increasing the heating time of the treatment, even when the heatingtemperature is comparatively low, the separability equivalent to thatobtained in heating at a high temperature can be obtained in some cases.Therefore, in the case where the heating temperature cannot be increasedbecause of the structure of the heating apparatus, it is preferable toincrease the heating time of the treatment.

The heating time of the first heat treatment is preferably longer thanor equal to 5 minutes and shorter than or equal to 24 hours, furtherpreferably longer than or equal to 30 minutes and shorter than or equalto 12 hours, still further preferably longer than or equal to 1 hour andshorter than or equal to 6 hours, for example. Note that the heatingtime of the first heat treatment is not limited to this. The heatingtime of the first heat treatment may be shorter than 5 minutes in thecase where the first heat treatment is performed by rapid thermalannealing (RTA), for example.

As the heating apparatus, any of a variety of apparatuses, e.g., anelectric furnace or an apparatus for heating an object by heatconduction or heat radiation from a heating element such as a resistanceheating element, can be used. For example, an RTA apparatus such as agas rapid thermal annealing (GRTA) apparatus or a lamp rapid thermalannealing (LRTA) apparatus can be used. An LRTA apparatus is anapparatus for heating an object by radiation of light (anelectromagnetic wave) emitted from a lamp such as a halogen lamp, ametal halide lamp, a xenon arc lamp, a carbon arc lamp, a high pressuresodium lamp, or a high pressure mercury lamp. The GRTA apparatus is anapparatus for heat treatment using a high-temperature gas. With the RTAapparatus, the process time can be shortened and thus the RTA apparatusis preferred for mass production. Alternatively, an in-line heatingapparatus may be used in the heat treatment.

In the case where a resin is used in a planarization layer or the likeof the display device, for example, heating is generally performed underthe conditions where oxygen is hardly contained and at the lowesttemperature in a temperature range in which the resin is cured, therebypreventing change in quality of the resin due to oxidation. In contrast,in one embodiment of the present invention, heating is performed at acomparatively high temperature (e.g., a temperature higher than or equalto 200° C.) with a surface of the first layer 24 a to be the first resinlayer 23 a exposed to an atmosphere positively containing oxygen. Thus,the first resin layer 23 a can have high separability.

Note that by the heat treatment, the thickness of the first resin layer23 a is changed from the thickness of the first layer 24 a in somecases. For example, by the removal of a solvent contained in the firstlayer 24 a or density increase due to the increase in stiffness, thevolume is decreased, so that the thickness of the first resin layer 23 abecomes smaller than the thickness of the first layer 24 a in somecases. Alternatively, owing to oxygen contained at the time ofperforming the heat treatment, the volume is increased, so that thethickness of the first resin layer 23 a becomes larger than thethickness of the first layer 24 a in some cases.

Before the first heat treatment is performed, thermal treatment (alsoreferred to as pre-baking treatment) for removing a solvent contained inthe first layer 24 a may be performed. The temperature of the pre-bakingtreatment can be determined as appropriate in consideration of amaterial to be used. The pre-baking treatment can be performed at atemperature of, for example, higher than or equal to 50° C. and lowerthan or equal to 180° C., higher than or equal to 80° C. and lower thanor equal to 150° C., or higher than or equal to 90° C. and lower than orequal to 120° C. The first heat treatment may also serve as thepre-baking treatment; that is, a solvent contained in the first layer 24a may be removed by the first heat treatment.

The first resin layer 23 a has flexibility. The formation substrate 14has lower flexibility than the first resin layer 23 a.

The first resin layer 23 a preferably has a thickness greater than orequal to 0.01 μm and less than 10 μm, further preferably greater than orequal to 0.1 μm and less than or equal to 3 μm, and still furtherpreferably greater than or equal to 0.5 μm and less than or equal to 2μm. With the use of a solution with low viscosity, the first resin layer23 a can be easily made thin. When the first resin layer 23 a has athickness in the above range, the display device can have higherflexibility. The force required for separating the first resin layer 23a is found to be small when the thickness of the first resin layer 23 ais large (see Example 2). Accordingly, the first resin layer 23 apreferably has a thickness of 1 μm or more. The thickness of the firstresin layer 23 a is not limited thereto, and may be greater than orequal to 10 μm. For example, the first resin layer 23 a may have athickness greater than or equal to 10 μm and less than or equal to 200μm. The first resin layer 23 a having a thickness greater than or equalto 10 μm is favorable because the rigidity of the display device can beincreased.

The first resin layer 23 a preferably has a thermal expansioncoefficient greater than or equal to 0.1 ppm/° C. and less than or equalto 50 ppm/° C., further preferably greater than or equal to 0.1 ppm/° C.and less than or equal to 20 ppm/° C., still further preferably greaterthan or equal to 0.1 ppm/° C. and less than or equal to 10 ppm/° C. Asthe first resin layer 23 a has a lower thermal expansion coefficient,generation of a crack in a layer included in a transistor or the likeand breakage of a transistor or the like which are caused owing to theheat treatment can be further prevented.

In the case where the first resin layer 23 a is positioned on thedisplay surface side of the display device, the first resin layer 23 apreferably has a high visible-light transmitting property.

Next, an insulating layer 31 is formed over the first resin layer 23 a(FIG. 1C).

The insulating layer 31 is formed at a temperature lower than or equalto the heat resistant temperature of the first resin layer 23 a. Theinsulating layer 31 is preferably formed at a temperature lower than orequal to the temperature of the first heat treatment and may be formedat a temperature lower than the temperature of the first heat treatment.

The insulating layer 31 can be used as a barrier layer that preventsimpurities contained in the first resin layer 23 a from diffusing into atransistor and a display element formed later. For example, theinsulating layer 31 preferably prevents moisture and the like containedin the first resin layer 23 a from diffusing into the transistor and thedisplay element when the first resin layer 23 a is heated. Thus, theinsulating layer 31 preferably has a high barrier property.

For the insulating layer 31, an inorganic insulating film such as asilicon nitride film, a silicon oxynitride film, a silicon oxide film, asilicon nitride oxide film, an aluminum oxide film, or an aluminumnitride film can be used, for example. A hafnium oxide film, a yttriumoxide film, a zirconium oxide film, a gallium oxide film, a tantalumoxide film, a magnesium oxide film, a lanthanum oxide film, a ceriumoxide film, a neodymium oxide film, or the like may be used. A stackincluding two or more of the above insulating films may also be used. Itis particularly preferable that a silicon nitride film be formed overthe first resin layer 23 a and a silicon oxide film be formed over thesilicon nitride film.

Note that in this specification and the like, silicon oxynitridecontains more oxygen than nitrogen, and silicon nitride oxide containsmore nitrogen than oxygen.

An inorganic insulating film is preferably formed at high temperaturesbecause the film can have higher density and barrier property as thedeposition temperature becomes higher.

The substrate temperature during the deposition of the insulating layer31 is preferably higher than or equal to room temperature (25° C.) andlower than or equal to 350° C., further preferably higher than or equalto 100° C. and lower than or equal to 300° C.

Next, a transistor 40 is formed over the insulating layer 31 (FIG. 1C).

There is no particular limitation on the structure of the transistor inthe display device. For example, a planar transistor, a staggeredtransistor, or an inverted staggered transistor may be used. A top-gatetransistor or a bottom-gate transistor may be used. Gate electrodes maybe provided above and below a channel.

Here, the case where a bottom-gate transistor including a metal oxidelayer 44 is formed as the transistor 40 is described. The metal oxidelayer 44 can serve as a semiconductor layer of the transistor 40. Metaloxide can serve as an oxide semiconductor.

In this embodiment, an oxide semiconductor is used as a semiconductor inthe transistor. A semiconductor material having a wider band gap and alower carrier density than silicon is preferably used because off-statecurrent of the transistor can be reduced.

The transistor 40 is formed at a temperature lower than or equal to theheat resistant temperature of the first resin layer 23 a. The transistor40 is preferably formed at a temperature lower than or equal to thetemperature of the first heat treatment and may be formed at atemperature lower than the temperature of the first heat treatment.

Specifically, first, a conductive layer 41 is formed over the insulatinglayer 31. The conductive layer 41 can be formed in the following manner:a conductive film is formed, a resist mask is formed, the conductivefilm is etched, and the resist mask is removed.

The substrate temperature during the deposition of the conductive filmis preferably higher than or equal to room temperature and lower than orequal to 350° C., further preferably higher than or equal to roomtemperature and lower than or equal to 300° C.

The conductive layers included in the display device can each have asingle-layer structure or a stacked-layer structure including any ofmetals such as aluminum, titanium, chromium, nickel, copper, yttrium,zirconium, molybdenum, silver, tantalum, and tungsten or an alloycontaining any of these metals as its main component. Alternatively, alight-transmitting conductive material such as indium oxide, indium tinoxide (ITO), indium oxide containing tungsten, indium zinc oxidecontaining tungsten, indium oxide containing titanium, ITO containingtitanium, indium zinc oxide, zinc oxide (ZnO), ZnO containing gallium,or ITO containing silicon may be used. Alternatively, a semiconductorsuch as an oxide semiconductor or polycrystalline silicon whoseresistance is lowered by containing an impurity element or the like, orsilicide such as nickel silicide may be used. A film including graphenemay be used as well. The film including graphene can be formed, forexample, by reducing a film containing graphene oxide. A semiconductorsuch as an oxide semiconductor containing an impurity element may beused. Alternatively, the film including graphene may be formed using aconductive paste of silver, carbon, copper, or the like or a conductivepolymer such as a polythiophene. A conductive paste is preferablebecause it is inexpensive. A conductive polymer is preferable because itis easily applied.

Next, an insulating layer 32 is formed. For the insulating layer 32, thedescription of the inorganic insulating film that can be used for theinsulating layer 31 can be referred to.

Then, the metal oxide layer 44 is formed. The metal oxide layer 44 canbe formed in the following manner: a metal oxide film is formed, aresist mask is formed, the metal oxide film is etched, and the resistmask is removed.

The substrate temperature during the deposition of the metal oxide filmis preferably lower than or equal to 350° C., further preferably higherthan or equal to room temperature and lower than or equal to 200° C.,still further preferably higher than or equal to room temperature andlower than or equal to 130° C.

The metal oxide film can be formed using one of or both an inert gas andan oxygen gas. Note that there is no particular limitation on the flowrate ratio of oxygen (the partial pressure of oxygen) during thedeposition of the metal oxide film. To obtain a transistor having highfield-effect mobility, the percentage of oxygen flow rate (the partialpressure of oxygen) during the deposition of the metal oxide film ispreferably higher than or equal to 0% and lower than or equal to 30%,further preferably higher than or equal to 5% and lower than or equal to30%, still further preferably higher than or equal to 7% and lower thanor equal to 15%.

The metal oxide film preferably contains at least indium or zinc. Inparticular, indium and zinc are preferably contained.

The energy gap of the metal oxide is preferably 2 eV or more, furtherpreferably 2.5 eV or more, and still further preferably 3 eV or more.With the use of metal oxide having such a wide energy gap, the off-statecurrent of the transistor can be reduced.

Such a metal oxide film can be formed by a sputtering method.Alternatively, a PLD method, a PECVD method, a thermal CVD method, anALD method, a vacuum evaporation method, or the like may be used.

Next, a conductive layer 43 a and a conductive layer 43 b are formed.The conductive layers 43 a and 43 b can be formed in the followingmanner: a conductive film is formed, a resist mask is formed, theconductive film is etched, and the resist mask is removed. Each of theconductive layers 43 a and 43 b is connected to the metal oxide layer44.

Note that during the processing of the conductive layers 43 a and 43 b,the metal oxide layer 44 might be partly etched to be thin in a regionnot covered by the resist mask.

The substrate temperature during the deposition of the conductive filmis preferably higher than or equal to room temperature and lower than orequal to 350° C., further preferably higher than or equal to roomtemperature and lower than or equal to 300° C.

In the above manner, the transistor 40 can be formed (FIG. 1C). In thetransistor 40, part of the conductive layer 41 functions as a gate, partof the insulating layer 32 functions as a gate insulating layer, and theconductive layer 43 a and the conductive layer 43 b function as a sourceand a drain.

After that, an insulating layer 33 that covers the transistor 40 isformed (FIG. 1D). The insulating layer 33 can be formed in a mannersimilar to that of the insulating layer 31.

It is preferable to use an oxide insulating film, such as a siliconoxide film or a silicon oxynitride film, formed in an atmospherecontaining oxygen for the insulating layer 33. An insulating film withlow oxygen diffusibility and oxygen permeability, such as a siliconnitride film, is preferably stacked over the silicon oxide film or thesilicon oxynitride film. The oxide insulating film formed in anatmosphere containing oxygen can easily release a large amount of oxygenby heating. When a stack including such an oxide insulating film thatreleases oxygen and an insulating film with low oxygen diffusibility andoxygen permeability is heated, oxygen can be supplied to the metal oxidelayer 44. As a result, oxygen vacancies in the metal oxide layer 44 canbe filled and defects at the interface between the metal oxide layer 44and the insulating layer 33 can be repaired, leading to a reduction indefect levels. Accordingly, an extremely highly reliable display devicecan be fabricated.

Through the above steps, the insulating layer 31, the transistor 40, andthe insulating layer 33 can be formed over the first resin layer 23 a(FIG. 1D).

If the formation substrate 14 and the transistor 40 are separated fromeach other at this stage by a method described later, a device includingno display element can be manufactured. For example, the transistor 40is formed, a capacitor, a resistor, a wiring, and the like are formed inaddition to the transistor 40, and the formation substrate 14 and thetransistor 40 are separated from each other by a method described later,so that a semiconductor device can be manufactured, for example.

Then, an insulating layer 34 is formed over the insulating layer 33(FIG. 1D). The display element is formed on the insulating layer 34 in alater step; thus, the insulating layer 34 preferably functions as aplanarization layer. For the insulating layer 34, the description of theorganic insulating film or the inorganic insulating film that can beused for the insulating layer 31 can be referred to.

The insulating layer 34 is formed at a temperature lower than or equalto the heat resistant temperature of the first resin layer 23 a. Theinsulating layer 34 is preferably formed at a temperature lower than orequal to the temperature of the first heat treatment and may be formedat a temperature lower than the temperature of the first heat treatment.

In the case of using an organic insulating film for the insulating layer34, a temperature applied to the first resin layer 23 a at the formationof the insulating layer 34 is preferably higher than or equal to roomtemperature and lower than or equal to 350° C. and further preferablyhigher than or equal to room temperature and lower than or equal to 300°C.

In the case of using an inorganic insulating film for the insulatinglayer 34, substrate temperature during the deposition is preferablyhigher than or equal to room temperature and lower than or equal to 350°C., and further preferably higher than or equal to 100° C. and lowerthan or equal to 300° C.

Next, an opening reaching the conductive layer 43 b is formed in theinsulating layer 34 and the insulating layer 33.

Then, a conductive layer 61 is formed (FIG. 1E). Part of the conductivelayer 61 functions as a pixel electrode of the light-emitting element60. The conductive layer 61 can be formed in the following manner: aconductive film is formed, a resist mask is formed, the conductive filmis etched, and the resist mask is removed.

The conductive layer 61 is formed at a temperature lower than or equalto the heat resistant temperature of the first resin layer 23 a. Theconductive layer 61 is preferably formed at a temperature lower than orequal to the temperature of the first heat treatment and may be formedat a temperature lower than the temperature of the first heat treatment.

The substrate temperature during the deposition of the conductive filmis preferably higher than or equal to room temperature and lower than orequal to 350° C., further preferably higher than or equal to roomtemperature and lower than or equal to 300° C.

Then, an insulating layer 35 that covers an end portion of theconductive layer 61 is formed (FIG. 1E). For the insulating layer 35,the description of the organic insulating film or the inorganicinsulating film that can be used for the insulating layer 31 can bereferred to.

The insulating layer 35 is formed at a temperature lower than or equalto the heat resistant temperature of the first resin layer 23 a. Theinsulating layer 35 is preferably formed at a temperature lower than orequal to the temperature of the first heat treatment and may be formedat a temperature lower than the temperature of the first heat treatment.

In the case of using an organic insulating film for the insulating layer35, a temperature applied to the first resin layer 23 a at the formationof the insulating layer 35 is preferably higher than or equal to roomtemperature and lower than or equal to 350° C. and further preferablyhigher than or equal to room temperature and lower than or equal to 300°C.

In the case of using an inorganic insulating film for the insulatinglayer 35, substrate temperature during the deposition is preferablyhigher than or equal to room temperature and lower than or equal to 350°C., and further preferably higher than or equal to 100° C. and lowerthan or equal to 300° C.

Then, an EL layer 62 and a conductive layer 63 are formed (FIG. 2A).Part of the conductive layer 63 functions as a common electrode of thelight-emitting element 60.

The EL layer 62 can be formed by an evaporation method, a coatingmethod, a printing method, a discharge method, or the like. In the casewhere the EL layer 62 is formed for each individual pixel, anevaporation method using a blocking mask such as a metal mask, anink-jet method, or the like can be used. In the case of sharing the ELlayer 62 by some pixels, an evaporation method not using a metal maskcan be used.

Either a low molecular compound or a high molecular compound can be usedfor the EL layer 62, and an inorganic compound may also be included.

The conductive layer 63 can be formed by an evaporation method, asputtering method, or the like.

The conductive layer 63 is formed at a temperature lower than or equalto the heat resistant temperature of the first resin layer 23 a andlower than or equal to the heat resistant temperature of the EL layer62. The conductive layer 63 is preferably formed at a temperature lowerthan or equal to the temperature of the first heat treatment and may beformed at a temperature lower than the temperature of the first heattreatment.

In the above manner, the light-emitting element 60 can be completed(FIG. 2A). In the light-emitting element 60, the conductive layer 61part of which functions as a pixel electrode, the EL layer 62, and theconductive layer 63 part of which functions as a common electrode arestacked.

Although a top-emission light-emitting element is formed as thelight-emitting element 60 here, one embodiment of the present inventionis not limited thereto.

The light-emitting element may be a top-emission, bottom-emission, ordual-emission light-emitting element. A conductive film that transmitsvisible light is used as the electrode through which light is extracted.A conductive film that reflects visible light is preferably used as theelectrode through which light is not extracted.

Then, an insulating layer 74 is formed covering the conductive layer 63(FIG. 2B). The insulating layer 74 functions as a protective layer thatprevents diffusion of impurities such as water into the light-emittingelement 60. The light-emitting element 60 is sealed with the insulatinglayer 74. After the conductive layer 63 is formed, the insulating layer74 is preferably formed without exposure to the air.

The insulating layer 74 is formed at a temperature lower than or equalto the heat resistant temperature of the first resin layer 23 a andlower than or equal to the heat resistant temperature of thelight-emitting element 60. The insulating layer 74 is preferably formedat a temperature lower than or equal to the temperature of the firstheat treatment and may be formed at a temperature lower than thetemperature of the first heat treatment.

The insulating layer 74 preferably includes an inorganic insulating filmwith a high barrier property that can be used for the insulating layer31. A stack including an inorganic insulating film and an organicinsulating film can also be used.

The insulating layer 74 can be formed by an ALD method, a sputteringmethod, or the like. An ALD method and a sputtering method arepreferable because a film can be formed at low temperatures. An ALDmethod is preferable because the coverage of the insulating layer 74 isimproved.

Then, a protective layer 75 is formed over the insulating layer 74 (FIG.2C). The protective layer 75 can be used as a layer positioned on theoutermost surface of the display device. The protective layer 75preferably has a high visible-light transmitting property.

The above-described organic insulating film that can be used for theinsulating layer 31 is preferably used for the protective layer 75because the surface of the display device can be prevented from beingdamaged or cracked.

FIG. 3A illustrates an example in which a substrate 75 a is attached tothe insulating layer 74 with a bonding layer 75 b.

As the bonding layer 75 b, any of a variety of curable adhesives such asa reactive curable adhesive, a thermosetting adhesive, an anaerobicadhesive, and a photocurable adhesive such as an ultraviolet curableadhesive can be used. Still alternatively, an adhesive sheet or the likemay be used.

For the substrate 75 a, a polyester resin such as polyethyleneterephthalate (PET) or polyethylene naphthalate (PEN), apolyacrylonitrile resin, an acrylic resin, a polyimide resin, apolymethyl methacrylate resin, a polycarbonate (PC) resin, apolyethersulfone (PES) resin, a polyamide resin (e.g., nylon or aramid),a polysiloxane resin, a cycloolefin resin, a polystyrene resin, apolyamide-imide resin, a polyurethane resin, a polyvinyl chloride resin,a polyvinylidene chloride resin, a polypropylene resin, apolytetrafluoroethylene (PTFE) resin, an ABS resin, or cellulosenanofiber can be used, for example. The substrate 75 a formed using anyof a variety of materials such as glass, quartz, a resin, a metal, analloy, and a semiconductor may be thin enough to be flexible.

Then, the formation substrate 14 and the first resin layer 23 a areseparated from each other (FIG. 3B).

For example, the first resin layer 23 a can be separated from theformation substrate 14 by applying a perpendicular tensile force to thefirst resin layer 23 a. Specifically, the first resin layer 23 a can beseparated from the formation substrate 14 by pulling up the substrate 75a by part of its suction-attached top surface.

Here, if separation is performed in such a manner that liquid containingwater such as water or an aqueous solution is added to the separationinterface and the liquid penetrates into the separation interface,separation can be easily performed. Furthermore, an adverse effect ofstatic electricity caused at separation on the functional element suchas a transistor (e.g., damage to a semiconductor element from staticelectricity) can be suppressed.

Before the separation, a separation starting point may be formed byseparating part of the first resin layer 23 a from the formationsubstrate 14. For example, a separation starting point may be formed byinserting a sharp instrument such as a knife between the formationsubstrate 14 and the first resin layer 23 a. Alternatively, a separationstarting point may be formed by cutting the first resin layer 23 a fromthe substrate 75 a side with a sharp instrument. The separation startingpoint may be formed by a method using a laser such as a laser ablationmethod.

In the manufacturing method example 1, the first heat treatment isperformed in the atmosphere containing oxygen at the time of forming thefirst resin layer 23 a; thus, the formation substrate 14 and the firstresin layer 23 a can be separated from each other without performinglaser irradiation on the entire surface of the first resin layer 23 a.Consequently, the display device can be manufactured at low cost.

The first resin layer 23 a that is exposed by being separated from theformation substrate 14 may be attached to a substrate 29 using a bondinglayer 28 (FIG. 3C). The substrate 29 can serve as a support substrate ofthe display device.

The material that can be used for the bonding layer 75 b can be used forthe bonding layer 28. The material that can be used for the substrate 75a can be used for the substrate 29.

Through the above steps, the display device using metal oxide for thechannel formation region of the transistor and a separate coloringmethod for an EL element can be fabricated.

Manufacturing Method Example 2

In a manufacturing method example given below, description of a portionsimilar to that in the above-described manufacturing method example isomitted in some cases.

First, the first layer 24 a is formed over the formation substrate 14(FIG. 4A).

For a material and a method that are used to form the first layer 24 a,the manufacturing method example 1 can be referred to.

In this embodiment, the first layer 24 a is formed using aphotosensitive and thermosetting material. Note that the first layer 24a may be formed using a non-photosensitive material.

Heat treatment (prebaking treatment) for removing a solvent is performedafter formation of the first layer 24 a, and then light exposure isperformed using a photomask. Next, development is performed, whereby anunnecessary portion can be removed. Subsequently, the first heattreatment is performed on the first layer 24 a that has been processedinto a desired shape, so that the first resin layer 23 a is formed (FIG.4B). In the example illustrated in FIG. 4B, the first resin layer 23 ahaving an island-like shape is formed.

Note that the first resin layer 23 a is not necessarily in the form of asingle island and may be in the form of a plurality of islands or havean opening, for example. In addition, unevenness may be formed on thesurface of the first resin layer 23 a by an exposure technique using ahalf-tone mask or a gray-tone mask, a multiple exposure technique, orthe like.

A mask such as a resist mask or a hard mask is formed over the firstlayer 24 a or the first resin layer 23 a and etching is performed,whereby the first resin layer 23 a with a desired shape can be formed.This method is particularly suitable for the case of using anon-photosensitive material. The mask is preferably formed to beextremely thin so that it can be removed at the same time as it isetched, in which case the step of removing the mask can be omitted.

In a manner similar to that of the manufacturing method example 1, thefirst heat treatment is performed in an atmosphere containing oxygen.The first heat treatment is preferably performed while supplying a gascontaining oxygen.

Then, a second layer 24 b is formed over the formation substrate 14 andthe first resin layer 23 a (FIG. 4C). A portion where the first resinlayer 23 a is not provided exists over the formation substrate 14. Thus,a portion that is in contact with the second layer 24 b can be formed onthe formation substrate 14.

The second layer 24 b can be formed using a material and a method thatcan be used to form the first layer 24 a.

The second layer 24 b is preferably formed by a coating method, in whichcase step coverage is improved and a surface of a second resin layer 23b described later can be flat.

The second layer 24 b is preferably formed using a thermosettingmaterial.

The second layer 24 b may be formed using a material havingphotosensitivity or a material that does not have photosensitivity.

In this embodiment, the second layer 24 b is formed using aphotosensitive and thermosetting material.

Subsequently, the second heat treatment is performed on the second resinlayer 24 b, so that the second resin layer 23 b is formed (FIG. 4D1).

The second heat treatment is performed in an atmosphere containing lessoxygen than the atmosphere of the first heat treatment. The second heattreatment is preferably performed without supplying a gas containingoxygen or while supplying a gas whose proportion of oxygen is lower thanthat of a gas used in the first heat treatment.

The second heat treatment can be performed in a state where theatmosphere in a chamber of an apparatus is a nitrogen atmosphere or arare gas atmosphere, for example.

The partial pressure of oxygen in performing the first heat treatment ispreferably higher than or equal to 0% and lower than 15%, furtherpreferably higher than or equal to 0% and lower than or equal to 10%,still further preferably higher than or equal to 0% and lower than orequal to 5%.

The second heat treatment is preferably performed while a gas that doesnot contain oxygen or a gas in which the proportion of oxygen is lowerthan the proportion of oxygen in the gas used in the first heattreatment is supplied into the chamber of the apparatus. The second heattreatment is preferably performed while only a nitrogen gas, only anargon gas, or a mixed gas containing oxygen is supplied. Specifically, amixed gas containing oxygen and nitrogen or a rare gas (e.g., argon) canbe used. The proportion of the flow rate of the oxygen gas in the flowrate of the whole mixed gas is preferably higher than 0% and lower than15%, further preferably higher than 0% and lower than or equal to 10%,still further preferably higher than 0% and lower than or equal to 5%.

The temperature of the second heat treatment is preferably higher thanor equal to 200° C. and lower than or equal to 500° C., furtherpreferably higher than or equal to 250° C. and lower than or equal to475° C., still further preferably higher than or equal to 300° C. andlower than or equal to 450° C.

By the second heat treatment, released gas components (e.g., hydrogen orwater) in the second resin layer 23 b can be reduced. In particular,heating is preferably performed at a temperature higher than or equal tothe formation temperature of each layer formed over the second resinlayer 23 b. Thus, a gas released from the second resin layer 23 b in themanufacturing process of the transistor can be significantly reduced.

For example, in the case where the manufacturing temperature of thetransistor is below 350° C., a film to be the second resin layer 23 b ispreferably heated at a temperature higher than or equal to 350° C. andlower than or equal to 450° C., further preferably lower than or equalto 400° C., still further preferably lower than or equal to 375° C.Thus, a gas released from the second resin layer 23 b in themanufacturing process of the transistor can be significantly reduced.

The maximum temperature in manufacturing the transistor is preferablyequal to the temperature of the second heat treatment, in which case themaximum temperature in manufacturing the device can be prevented frombeing increased by the second heat treatment.

The longer the second heat treatment time is, the more sufficientlyreleased gas components in the second resin layer 23 b can be reduced.

By increasing the heating time of the heat treatment, even when theheating temperature is comparatively low, an effect equivalent to thatobtained in heating at a high temperature can be obtained in some cases.Therefore, in the case where the heating temperature cannot be increasedbecause of the structure of the apparatus, it is preferable to increasethe heating time of the treatment.

The heating time of the second heat treatment is preferably longer thanor equal to 5 minutes and shorter than or equal to 24 hours, furtherpreferably longer than or equal to 30 minutes and shorter than or equalto 12 hours, still further preferably longer than or equal to 1 hour andshorter than or equal to 6 hours, for example. Note that the heatingtime of the second heat treatment is not limited to this. The heatingtime of the second heat treatment may be shorter than 5 minutes in thecase where the second heat treatment is performed by RTA, for example.

Note that by the heat treatment, the thickness of the second resin layer23 b is changed from the thickness of the second layer 24 b in somecases.

Before the second heat treatment is performed, thermal treatment(pre-baking treatment) for removing a solvent contained in the secondlayer 24 b may be performed. The second heat treatment may also serve asthe pre-baking treatment; that is, a solvent contained in the secondlayer 24 b may be removed by the second heat treatment.

The second resin layer 23 b has flexibility. The formation substrate 14has lower flexibility than the second resin layer 23 b.

The second resin layer 23 b preferably has a thickness greater than orequal to 0.01 μm and less than 10 μm, further preferably greater than orequal to 0.1 μm and less than or equal to 3 μm, and still furtherpreferably greater than or equal to 0.5 μm and less than or equal to 2μm. With the use of a solution having low viscosity, the second resinlayer 23 b having a small thickness can be easily formed. When thesecond resin layer 23 b has a thickness in the above range, the displaydevice can have higher flexibility. The thickness of the second resinlayer 23 b is found not to affect the force required for separating thefirst resin layer 23 a (see Example 2). Thus, it is considered that thesecond resin layer 23 b can be formed thinner than the first resin layer23 a. Without being limited thereto, the thickness of the second resinlayer 23 b may be greater than or equal to 10 μm. For example, thesecond resin layer 23 b may have a thickness greater than or equal to 10μm and less than or equal to 200 μm. The second resin layer 23 b thathas a thickness greater than or equal to 10 μm is favorable because therigidity of the display device can be increased.

The second resin layer 23 b preferably has a thermal expansioncoefficient greater than or equal to 0.1 ppm/° C. and less than or equalto 50 ppm/° C., further preferably greater than or equal to 0.1 ppm/° C.and less than or equal to 20 ppm/° C., still further preferably greaterthan or equal to 0.1 ppm/° C. and less than or equal to 10 ppm/° C. Asthe second resin layer 23 b has a lower thermal expansion coefficient,generation of a crack in a layer included in a transistor or the likeand breakage of a transistor or the like which are caused owing to theheat treatment can be further prevented.

In the case where the second resin layer 23 b is positioned on thedisplay surface side of the display device, the second resin layer 23 bpreferably has a high visible-light transmitting property.

The second resin layer 23 b that does not have a planarizing functionmay be used. Although the second resin layer 23 b has a flat top surfacein an example shown in FIG. 4D1, the second resin layer 23 b may have anuneven top surface as shown in FIG. 4D2.

Although the second resin layer 23 b shown in FIG. 4D1 has an angularshape, the second resin layer 23 b as well as the first resin layer 23 amay have a tapered end portion.

The first resin layer 23 a and the second resin layer 23 b may be formedusing different materials or the same material. The same material ispreferably used because the cost can be reduced. Even when the samematerial is used, the degree of adhesion between the formation substrate14 and the first resin layer 23 a can be made different from thatbetween the formation substrate 14 and the second resin layer 23 b byperforming the first treatment and the second heat treatment underdifferent conditions.

Next, the insulating layer 31 is formed over the second resin layer 23 b(FIG. 4E).

The insulating layer 31 is formed at a temperature lower than or equalto the heat resistance temperature of the first resin layer 23 a andlower than or equal to the heat resistance temperature of the secondresin layer 23 b. The insulating layer 31 is preferably formed at atemperature lower than or equal to the temperature of the first heattreatment and lower than or equal to the temperature of the second heattreatment and may be formed at a temperature lower than both of thetemperature of the first heat treatment and the temperature of thesecond heat treatment.

The insulating layer 31 can be used as a barrier layer that preventsdiffusion of impurities contained in the first resin layer 23 a and thesecond resin layer 23 b into a transistor and a display element formedlater. For example, the insulating layer 31 preferably prevents moistureand the like contained in the first resin layer 23 a and the secondresin layer 23 b from diffusing into the transistor and the displayelement when the first resin layer 23 a and the second resin layer 23 bare heated. Thus, the insulating layer 31 preferably has a high barrierproperty.

For the insulating layer 31, the material given as an example in themanufacturing method example 1 can be used.

Next, the transistor 40 is formed over the insulating layer 31 (FIG.4E).

The transistor 40 is formed at a temperature lower than or equal to theheat resistance temperature of the first resin layer 23 a and lower thanor equal to the heat resistance temperature of the second resin layer 23b. The transistor 40 is preferably formed at a temperature lower than orequal to the temperature of the first heat treatment and lower than orequal to the temperature of the second heat treatment and may be formedat a temperature lower than both of the temperature of the first heattreatment and the temperature of the second heat treatment.

Then, in a manner similar to that described in the manufacturing methodexample 1, constituents from the insulating layer 33 to the protectivelayer 75 are formed (FIG. 5A). Note that the constituents are formed ata temperature lower than or equal to the heat resistance temperature ofthe first resin layer 23 a and lower than or equal to the heatresistance temperature of the second resin layer 23 b. The constituentsare preferably formed at a temperature lower than or equal to thetemperature of the first heat treatment and lower than or equal to thetemperature of the second heat treatment and may be formed at atemperature lower than both of the temperature of the first heattreatment and the temperature of the second heat treatment.

Then, the separation starting point is formed in the first resin layer23 a (FIGS. 5B1 and 5B2).

For example, a sharp instrument 65 such as a knife is inserted from theprotective layer 75 side into a portion inward from an end portion ofthe first resin layer 23 a to form a frame-like-shaped cut 64.

The first resin layer 23 a may be irradiated with laser light in aframe-like shape.

In the manufacturing method example 2, a portion that is in contact withthe first resin layer 23 a and a portion that is in contact with thesecond resin layer 23 b are provided for the formation substrate 14. Bythe first heat treatment performed in the atmosphere containing oxygen,the first resin layer 23 a becomes easy to separate from the formationsubstrate 14. In contrast, the second resin layer 23 b is difficult toseparate from the formation substrate 14 because the second heattreatment is performed in the atmosphere containing less oxygen than theatmosphere of the first heat treatment. Thus, separation of the firstresin layer 23 a from the formation substrate 14 that will occur at anunintended time can be inhibited. Furthermore, the separation startingpoint enables separation of the formation substrate 14 and the firstresin layer 23 a from each other at a desired time. As a result, thetime at which the separation occurs can be controlled and highseparability can be achieved. This can improve the yield of theseparation process and the manufacturing process of the display device.

Then, the formation substrate 14 and the transistor 40 are separatedfrom each other (FIG. 6A).

In the manufacturing method example 2, the first heat treatment isperformed in the atmosphere containing oxygen at the time of forming thefirst resin layer 23 a; thus, the formation substrate 14 and the firstresin layer 23 a can be separated from each other without performinglaser irradiation on the entire surface of the first resin layer 23 a.Consequently, the display device can be manufactured at low cost.

Then, the first resin layer 23 a that is exposed by being separated fromthe formation substrate 14 is attached to the substrate 29 using thebonding layer 28 (FIG. 6B). The substrate 29 can serve as a supportsubstrate of the display device.

Through the above steps, the display device using metal oxide in thechannel formation region of the transistor and a separate coloringmethod for an EL element can be fabricated.

Structure Example 1 of Display Device

FIG. 7A is a top view of a display device 10A. FIGS. 7B and 7C showexamples of a cross-sectional view of a display portion 381 and across-sectional view of a connection portion for connection to an FPC372 in the display device 10A.

The display device 10A can be manufactured by the manufacturing methodexample 2. The display device 10A can remain being bent or can be bentrepeatedly, for example.

The display device 10A includes the protective layer 75 and thesubstrate 29. The protective layer 75 side corresponds to the displaysurface side of the display device. The display device 10A includes thedisplay portion 381 and a driver circuit portion 382. The FPC 372 isattached to the display device 10A.

A conductive layer 43 c is electrically connected to the FPC 372 througha connector 76 (FIGS. 7B and 7C). The conductive layer 43 c can beformed using the same material and the same step as those used to formthe source and the drain of the transistor.

As the connector 76, any of various anisotropic conductive films (ACF),anisotropic conductive pastes (ACP), and the like can be used.

The display device shown in FIG. 7C is different from the display deviceshown in FIG. 7B in that a transistor 49 is included instead of thetransistor 40 and that a coloring layer 97 is provided over theinsulating layer 33. In the case where the light-emitting element 60 isa bottom-emission type light-emitting element, the coloring layer 97 canbe provided closer to the substrate 29 than the light-emitting element60 is.

In the transistor 49 shown in FIG. 7C, a conductive layer 45 serving asa gate is added to the structure of the transistor 40 shown in FIG. 7B.

The structure in which the semiconductor layer where a channel is formedis provided between two gates is used as an example of the transistor49. Such a structure enables control of threshold voltages oftransistor. In that case, the two gates may be connected to each otherand supplied with the same signal to operate the transistor. Such atransistor can have a higher field-effect mobility and thus have higheron-state current than other transistors. Consequently, a circuit capableof high-speed operation can be obtained. Furthermore, the area occupiedby a circuit portion can be reduced. The use of the transistor havinghigh on-state current can reduce signal delay in wirings and can reducedisplay unevenness even in a display device in which the number ofwirings is increased because of increase in size or definition.

Alternatively, by supplying a potential for controlling the thresholdvoltage to one of the two gates and a potential for driving to theother, the threshold voltage of the transistor can be controlled.

As described above, by the heat treatment performed in the atmospherecontaining oxygen, the first resin layer 23 a can be separated from theformation substrate without performing laser irradiation on the entiresurface of the first resin layer 23 a. Therefore, in some cases, it isshown by analysis that a large amount of oxygen is contained in thefirst resin layer 23 a included in the display device manufactured bythe manufacturing method of the display device of this embodiment.Specifically, the oxygen concentration can be measured by analyzing,using XPS, a surface of the first resin layer 23 a on the separationsurface side (the surface is also referred to as the surface on theformation substrate side and corresponds to a surface in contact withthe bonding layer 28 in FIGS. 7B and 7C). In particular, the oxygenconcentration measured by the XPS analysis performed on the surface ofthe first resin layer 23 a on the bonding layer 28 side is preferablyhigher than or equal to 10 atomic %, further preferably higher than orequal to 15 atomic %.

Manufacturing Method Example 3

Although the first resin layer 23 a and the second resin layer 23 b areformed in the manufacturing method example 2, the second resin layer 23b is not necessarily provided depending on the level of adhesion betweenthe insulating layer 31 and the formation substrate 14.

Specifically, after the first resin layer 23 a is formed over theformation substrate 14, the insulating layer 31 may be formed in contactwith top surfaces of the formation substrate 14 and the first resinlayer 23 a. Then, constituents from the transistor 40 to the protectivelayer 75 are formed over the insulating layer 31 (FIG. 8A).

In the manufacturing method example 3, the portion that is in contactwith the first resin layer 23 a and a portion that is in contact withthe insulating layer 31 are provided for the formation substrate 14.When the formation substrate 14 and the insulating layer 31 adhere toeach other with sufficiently high adhesion, unintentional separation ofthe first resin layer 23 a from the formation substrate 14 can beinhibited even in the case where the first resin layer 23 a has highseparability. Furthermore, the separation starting point is formed (seethe instrument 65 shown in FIG. 8A), whereby the formation substrate 14and the first resin layer 23 a can be separated from each other at adesired time (FIG. 8B). As a result, the time at which the separationoccurs can be controlled and high separability can be achieved. This canimprove the yield of the separation process and the manufacturingprocess of the display device.

Manufacturing Method Example 4

First, constituents from the first resin layer 23 a to the insulatinglayer 35 are formed in order over the formation substrate 14 in a mannersimilar to that in the manufacturing method example 2 (FIG. 9A).

Then, the protective layer 71 is formed as illustrated in FIG. 9B.

The protective layer 71 has a function of protecting surfaces of theinsulating layer 35 and the conductive layer 61 in a separation step.The protective layer 71 can be formed using a material that can beeasily removed.

For the protective layer 71 that can be removed, a water-soluble resincan be used, for example. A water-soluble resin is applied to an unevensurface to cover the unevenness, which facilitates the protection of thesurface. A stack of a water-soluble resin and an adhesive that can beseparated by light or heat may be used for the protective layer 71 thatcan be removed.

For the protective layer 71 that can be removed, a base material havinga property in which adhesion is strong in a normal state but weakenedwhen irradiated with light or heated may be used. For example, a thermalseparation tape whose adhesion is weakened by heat, a UV-separation tapewhose adhesion is weakened by ultraviolet irradiation, or the like maybe used. Alternatively, a weak adhesion tape with weak adhesiveness in anormal state, or the like can be used.

Then, the formation substrate 14 and the transistor 40 are separatedfrom each other in a manner similar to that in the manufacturing methodexample 2 (FIG. 9C).

After the formation substrate 14 and the insulating layer 31 areseparated from each other, the protective layer 71 is removed.

Then, the EL layer 62 and the conductive layer 63 are formed, wherebythe light-emitting element 60 is obtained. Thus, by sealing thelight-emitting element 60, the display device can be obtained. Forsealing of the light-emitting element 60, one or more of the insulatinglayer 74, the protective layer 75, the substrate 75 a, the bonding layer75 b, and the like can be used.

Although the EL layer 62 and the conductive layer 63 may be formed whilethe first resin layer 23 a is fixed to a stage, they are preferablyformed while the first resin layer 23 a is fixed to a supportingsubstrate by a tape or the like and the supporting substrate is placedon the stage of the deposition apparatus. Fixing the first resin layer23 a to the supporting substrate can facilitate the transfer of thefirst resin layer 23 a in an apparatus and between apparatuses. Thesubstrate that can be used as the formation substrate 14 can be used asthe supporting substrate.

In the manufacturing method example 4, an EL layer or the like is formedafter the separation of the formation substrate 14, whereby the displayelement can be formed. In the case where the stacked layer structure ofthe EL layer and the like include a portion having a low adhesion,forming these layers after the separation can suppress a reduction inthe yield of separation. Thus, by using the manufacturing method example4, the material can be selected more freely, leading to fabrication of ahighly reliable display device at lower cost.

Manufacturing Method Example 5

First, the first island-shaped resin layer 23 a is formed over theformation substrate 14 in a manner similar to that in the manufacturingmethod example 2. Then, the second resin layer 23 b is formed over theformation substrate 14 and the first resin layer 23 a (FIG. 10A).

Specifically, the first layer 24 a is formed over the formationsubstrate 14, and a first heat treatment is performed on the first layer24 a having a desired shape, whereby the first resin layer 23 a isformed. The first heat treatment is performed in an atmospherecontaining oxygen. Then, the second layer 24 b is formed over theformation substrate 14 and the first resin layer 23 a, and a second heattreatment is performed on the second layer 24 b, whereby the secondresin layer 23 b is formed. The second heat treatment is performed in anatmosphere containing less oxygen than the atmosphere of the first heattreatment.

Next, the insulating layer 31 is formed over the second resin layer 23 bin a manner similar to that in manufacturing method example 2 (FIG.10B).

Then, a transistor 80 is formed over the insulating layer 31 (FIG. 10B).

Here, the case where a transistor including a metal oxide layer 83 andtwo gates is formed as the transistor 80 is described.

The transistor 80 is formed at a temperature lower than or equal to theheat resistance temperature of the first resin layer 23 a and lower thanor equal to the heat resistance temperature of the second resin layer 23b. The transistor 80 is preferably formed at a temperature lower than orequal to the temperature of the first heat treatment and lower than orequal to the temperature of the second heat treatment and may be formedat a temperature lower than both of the temperature of the first heattreatment and the temperature of the second heat treatment.

Specifically, first, a conductive layer 81 is formed over the insulatinglayer 31. The conductive layer 81 can be formed in the following manner:a conductive film is formed, a resist mask is formed, the conductivefilm is etched, and the resist mask is removed.

Next, an insulating layer 82 is formed. For the insulating layer 82, thedescription of the inorganic insulating film that can be used to formthe insulating layer 31 can be referred to.

Then, the metal oxide layer 83 is formed. The metal oxide layer 83 canbe formed in the following manner: a metal oxide film is formed, aresist mask is formed, the metal oxide film is etched, and the resistmask is removed. For the metal oxide layer 83, the description of thematerial that can be used for the metal oxide layer 44 can be referredto.

Then, an insulating layer 84 and a conductive layer 85 are formed. Forthe insulating layer 84, the description of the inorganic insulatingfilm that can be used to form the insulating layer 31 can be referredto. The insulating layer 84 and the conductive layer 85 can be formed inthe following manner: an insulating film to be the insulating layer 84and a conductive film to be the conductive layer 85 are formed, a resistmask is formed, the insulating film and the conductive film are etched,and the resist mask is removed.

Next, the insulating layer 33 that covers the metal oxide layer 83, theinsulating layer 84, and the conductive layer 85 is formed. Theinsulating layer 33 can be formed in a manner similar to that of formingthe insulating layer 31.

Note that the insulating layer 33 preferably contains hydrogen. Hydrogencontained in the insulating layer 33 diffuses into the metal oxide layer83 that is in contact with the insulating layer 33, so that theresistance of part of the metal oxide layer 83 is reduced. The metaloxide layer 83 that is in contact with the insulating layer 33 serves asa low-resistance region, and thus, the on-state current and thefield-effect mobility of the transistor 80 can be increased.

Then, openings reaching the metal oxide layer 83 are formed in theinsulating layer 33.

Then, a conductive layer 86 a and a conductive layer 86 b are formed.The conductive layers 86 a and 86 b can be formed in the followingmanner: a conductive film is formed, a resist mask is formed, theconductive film is etched, and the resist mask is removed. Theconductive layers 86 a and 86 b are electrically connected to the metaloxide layer 83 through the openings formed in the insulating layer 33.

In the above manner, the transistor 80 can be formed (FIG. 10B). In thetransistor 80, part of the conductive layer 81 functions as a gate, partof the insulating layer 84 functions as a gate insulating layer, part ofthe insulating layer 82 functions as a gate insulating layer, and partof the conductive layer 85 functions as a gate. The metal oxide layer 83includes a channel region and a low-resistance region. The channelregion overlaps with the conductive layer 85 with the insulating layer84 provided therebetween. The low-resistance region includes a regionconnected to the conductive layer 86 a and a region connected to theconductive layer 86 b.

Next, constituents from the insulating layer 34 to the light-emittingelement 60 are formed over the insulating layer 33 (FIG. 10C). For thesesteps, the description of the manufacturing method example 1 can bereferred to.

Furthermore, steps shown in FIGS. 11A and 11B are performedindependently of the steps shown in FIGS. 10A to 10C. As in the step offorming the first resin layer 23 a over the formation substrate 14, anisland-like-shaped first resin layer 93 a is formed over a formationsubstrate 91. Then, as in a step of forming the second resin layer 23 bover the formation substrate 14 and the first resin layer 23 a, a secondresin layer 93 b is formed over the formation substrate 91 and the firstresin layer 93 a (FIG. 11A).

Specifically, a first layer is formed over the formation substrate 91,and the first heat treatment is performed on the first layer having adesired shape, whereby the first resin layer 93 a is formed. The firstheat treatment is performed in an atmosphere containing oxygen. Then, asecond layer is formed over the formation substrate 91 and the firstresin layer 93 a, and the second heat treatment is performed on thesecond layer, whereby the second resin layer 93 b is formed. The secondheat treatment is performed in an atmosphere containing less oxygen thanan atmosphere of the first heat treatment.

The first resin layer 93 a and the second resin layer 93 b may be formedusing different materials or the same material. The same material ispreferably used because the cost can be reduced. Even when the samematerial is used, the degree of adhesion between the formation substrate91 and the first resin layer 93 a can be made different from thatbetween the formation substrate 91 and the second resin layer 93 b byperforming the first treatment and the second heat treatment underdifferent conditions.

The first resin layer 23 a, the second resin layer 23 b, the first resinlayer 93 a, and the second resin layer 93 b may be formed usingdifferent materials or the same material. The same material ispreferably used because the cost can be reduced. Even when the samematerial is used, the separability of the resin layers can be controlledby performing heat treatment on the resin layers under differentconditions.

Then, an insulating layer 95 is formed over the second resin layer 93 b.Then, the coloring layer 97 and a light-blocking layer 98 are formedover the insulating layer 95 (FIG. 11B).

For the insulating layer 95, the description of the insulating layer 31can be referred to.

A color filter or the like can be used as the coloring layer 97. Thecoloring layer 97 is provided to overlap with a display region of thelight-emitting element 60.

A black matrix or the like can be used as the light-blocking layer 98.The light-blocking layer 98 is provided to overlap with the insulatinglayer 35.

Next, a surface of the formation substrate 14 on which the transistor 80and the like are formed and a surface of the formation substrate 91 onwhich the coloring layer 97 and the like are formed are attached to eachother with a bonding layer 99 (FIG. 11C).

Then, the separation starting point is formed in the first resin layer23 a (FIGS. 12A and 12B). Either of the formation substrate 14 and theformation substrate 91 may be separated earlier. In the example shownhere, the formation substrate 14 is separated earlier than the formationsubstrate 91.

For example, the first resin layer 23 a is irradiated with laser light66 in a frame-like shape from the formation substrate 14 side (see alaser-light irradiation region 67 shown in FIG. 12B). This method issuitable in the case of using hard substrates such as glass substratesas the formation substrate 14 and the formation substrate 91.

There is no particular limitation on a laser used to form the separationstarting point. For example, a continuous wave laser or a pulsedoscillation laser can be used. Note that a condition for laserirradiation such as frequency, power density, energy density, or beamprofile is controlled as appropriate in consideration of thicknesses,materials, or the like of the formation substrate and the first resinlayer.

In the manufacturing method example 5, a portion that is in contact withthe first resin layer 23 a and a portion that is in contact with thesecond resin layer 23 b are provided for the formation substrate 14. Bythe first heat treatment performed in the atmosphere containing oxygen,the first resin layer 23 a becomes easy to separate from the formationsubstrate 14. In contrast, the second resin layer 23 b is difficult toseparate from the formation substrate 14 because the second heattreatment is performed in the atmosphere containing less oxygen than theatmosphere of the first heat treatment. Thus, separation of the firstresin layer 23 a from the formation substrate 14 that will occur at anunintended time can be inhibited. Similarly, a portion that is incontact with the first resin layer 93 a and a portion that is in contactwith the second resin layer 93 b are provided for the formationsubstrate 91. The first resin layer 93 a is easy to separate from theformation substrate 91, and the second resin layer 93 b is difficult toseparate from the formation substrate 91. Thus, separation of the firstresin layer 93 a from the formation substrate 91 that will occur at anunintended time can be inhibited.

A separation starting point is formed on either the first resin layer 23a or the first resin layer 93 a. The timing of forming a separationstarting point can be different between the first resin layer 23 a andthe first resin layer 93 a; therefore, the formation substrate 14 andthe formation substrate 91 can be separated in different steps. This canincrease the yield of the separation process and the manufacturingprocess of a display device.

Irradiation with the laser light 66 does not need to be performed on theentire area of the first resin layer 23 a and is performed on part ofthe resin layer. Accordingly, an expensive laser apparatus requiringhigh running costs is not needed.

Next, the formation substrate 14 and the transistor 80 are separatedfrom each other (FIG. 13A). In this example, the formation substrate 14and a portion inside the region irradiated with the laser light 66 in aframe-like shape (i.e., a portion inside the laser-light irradiationregion 67 illustrated in FIG. 12B) are separated from each other.Although in the example illustrated in FIG. 13A separation occurs in thebonding layer 99 (cohesive failure of the bonding layer 99 occurs)outside the region irradiated with the laser light 66 in a frame-likeshape, one embodiment of the present invention is not limited to thisexample. For example, outside the irradiation region 67, separation(interfacial failure or adhesive failure) might occur at the interfacebetween the bonding layer 99 and the insulating layer 95 or theinsulating layer 33.

In the manufacturing method example 5, the first heat treatment isperformed in the atmosphere containing oxygen at the time of forming thefirst resin layer 23 a; thus, the formation substrate 14 and the firstresin layer 23 a can be separated from each other without performinglaser irradiation on the entire surface of the first resin layer 23 a.Consequently, the display device can be manufactured at low cost.

Then, the first resin layer 23 a that is exposed by being separated fromthe formation substrate 14 is attached to the substrate 29 using thebonding layer 28 (FIG. 13B). The substrate 29 can serve as a supportsubstrate of the display device.

Then, the separation starting point is formed in the first resin layer93 a (FIG. 14A).

In FIG. 14A, the sharp instrument 65 such as a knife is inserted fromthe substrate 29 side into a portion inward from an end portion of thefirst resin layer 93 a to form a frame-like-shaped cut. This method issuitable in the case of using a resin as the substrate 29.

Alternatively, in a manner similar to that of the formation of theseparation starting point in the first resin layer 23 a, the first resinlayer 93 a may be irradiated with laser light in a frame-like shape fromthe formation substrate 91 side.

The separation starting point enables separation of the formationsubstrate 91 and the first resin layer 93 a from each other at a desiredtime. As a result, the time at which the separation occurs can becontrolled and high separability can be achieved. This can improve theyield of the separation process and the manufacturing process of thedisplay device.

Then, the formation substrate 91 and the transistor 80 are separatedfrom each other (FIG. 14B). In the example shown here, a portion insidethe frame-like-shaped cut is separated from the formation substrate 91.

In the manufacturing method example 5, the first heat treatment isperformed in the atmosphere containing oxygen at the time of forming thefirst resin layer 93 a; thus, the formation substrate 91 and the firstresin layer 93 a can be separated from each other without performinglaser irradiation on the entire surface of the first resin layer 93 a.Consequently, the display device can be manufactured at low cost.

Then, the first resin layer 93 a that is exposed by being separated fromthe formation substrate 91 is attached to a substrate 22 using a bondinglayer 13 (FIG. 15A). The substrate 22 can serve as a support substrateof the display device.

In FIG. 15A, light emitted from the light-emitting element 60 isextracted to the outside of the display device through the coloringlayer 97, the second resin layer 93 b, and the first resin layer 93 a.Therefore, the first resin layer 93 a and the second resin layer 93 beach preferably have a high visible light transmittance. In theseparation method of one embodiment of the present invention, thethickness of each of the first resin layer 93 a and the second resinlayer 93 b can be reduced. Thus, the first resin layer 93 a and thesecond resin layer 93 b can each have a high visible lighttransmittance, which can inhibit reduction of the light extractionefficiency of the light-emitting element 60.

One or both of the first resin layer 93 a and the second resin layer 93b may be removed. This can further increase the light extractionefficiency of the light-emitting element 60. In the example shown inFIG. 15B, both of the first resin layer 93 a and the second resin layer93 b are removed and the substrate 22 is attached to the insulatinglayer 95 with the bonding layer 13.

The material that can be used for the bonding layer 75 b can be used forthe bonding layer 13.

The material that can be used for the substrate 75 a can be used for thesubstrate 22.

The manufacturing method example 5 is an example in which the separationmethod of one embodiment of the present invention is performed twice tofabricate the display device. In one embodiment of the presentinvention, each of the functional elements and the like included in thedisplay device is formed over the formation substrate; thus, even in thecase where a high-resolution display device is manufactured, highalignment accuracy of a flexible substrate is not required. It is thuseasy to attach the flexible substrate.

Modification Example

In the manufacturing method example 5 (FIG. 11C), the bonding layer 99overlaps with both a portion where the formation substrate 14 and thesecond resin layer 23 b are in contact with each other and a portionwhere the formation substrate 91 and the second resin layer 93 b are incontact with each other.

The adhesion between the formation substrate 14 and the second resinlayer 23 b is higher than that between the formation substrate 14 andthe first resin layer 23 a. The adhesion between the formation substrate91 and the second resin layer 93 b is higher than that between theformation substrate 91 and the first resin layer 93 a.

When separation is caused at the interface between the formationsubstrate and the second resin layer, separation might be failed, forexample, reducing the yield of separation. Therefore, the process issuitable in which only the portion that overlaps with the first resinlayer is separated from the formation substrate after formation of aseparation starting point in the first resin layer in a frame-likeshape.

It is also possible to employ a structure in which the bonding layer 99does not overlap with the portion where the formation substrate 14 andthe second resin layer 23 b are in contact with each other and theportion where the formation substrate 91 and the second resin layer 93 bare in contact with each other, as illustrated in FIGS. 16A and 16B.

When an adhesive or an adhesive sheet having a low fluidity, forexample, is used for the bonding layer 99, the bonding layer 99 can beeasily formed to have an island-like shape (FIG. 16A).

Alternatively, a partition 98 a having a frame-like shape may be formedand the space surrounded by the partition 98 a may be filled with thebonding layer 99 (FIG. 16B).

In the case where the partition 98 a is used as a component of a displaydevice, the partition 98 a is preferably formed using a cured resin. Inthat case, it is preferable that the partition 98 a not overlap with theportion where the formation substrate 14 and the second resin layer 23 bare in contact with each other and the portion where the formationsubstrate 91 and the second resin layer 93 b are in contact with eachother, either.

In the case where the partition 98 a is not used as a component of adisplay device, the partition 98 a is preferably formed using an uncuredresin or a semi-cured resin. In that case, the partition 98 a mayoverlap with one or both of the portion where the formation substrate 14and the second resin layer 23 b are in contact with each other and theportion where the formation substrate 91 and the second resin layer 93 bare in contact with each other.

In the example described in this embodiment, the partition 98 a isformed using an uncured resin, and the partition 98 a does not overlapwith the portion where the formation substrate 14 and the second resinlayer 23 b are in contact with each other and the portion where theformation substrate 91 and the second resin layer 93 b are in contactwith each other.

Description is made on a method for forming a separation starting pointin the case where the bonding layer 99 does not overlap with the portionwhere the formation substrate 14 and the second resin layer 23 b are incontact with each other and the portion where the formation substrate 91and the second resin layer 93 b are in contact with each other. Here, anexample in which the formation substrate 91 is separated ahead of theformation substrate 14 is shown.

FIGS. 17A to 17E illustrate positions of irradiation with the laserlight 66 in the case where the formation substrate 91 and the firstresin layer 93 a are separated from each other.

As illustrated in FIG. 17A, at least one place of a region where thefirst resin layer 93 a and the bonding layer 99 overlap with each otheris irradiated with the laser light 66, whereby the separation startingpoint can be formed.

It is preferable that the force for separating the formation substrate91 and the first resin layer 93 a from each other be locally exerted onthe separation starting point; therefore, the separation starting pointis preferably formed in the vicinity of an end portion of the bondinglayer 99 rather than at the center of the bonding layer 99. It isparticularly preferable to form the separation starting point in thevicinity of the corner portion compared to the vicinity of the sideportion among the vicinities of the end portion.

FIGS. 17B to 17E illustrate examples of the laser-light irradiationregion 67.

In FIG. 17B, one laser-light irradiation region 67 is provided at thecorner portion of the bonding layer 99.

The separation starting point can be formed in the form of a solid lineor a dashed line by continuous or intermittent irradiation with laserlight. In FIG. 17C, three laser-light irradiation regions 67 areprovided at the corner portion of the bonding layer 99. FIG. 17Dillustrates an example in which the laser-light irradiation region 67abuts on and extends along one side of the bonding layer 99. Asillustrated in FIG. 17E, the laser-light irradiation region 67 may bepositioned not only in a region where the bonding layer 99 and the firstresin layer 93 a overlap with each other but also in a region where thepartition 98 a not cured and the first resin layer 93 a overlap witheach other.

Then, the formation substrate 91 and the first resin layer 93 a can beseparated from each other (FIG. 18A). Note that part of the partition 98a remains on the formation substrate 14 side in some cases. Thepartition 98 a may be removed or the next step may be performed withoutremoval of the partition 98 a. The partition 98 a is not illustrated forsimplicity.

Next, the substrate 22 and the first resin layer 93 a that is exposed bybeing separated from the formation substrate 91 are bonded to each otherusing the adhesive layer 13 (FIG. 18B).

The adhesive layer 13 as well as the adhesive layer 99 does not overlapwith a portion where the formation substrate 14 and the second resinlayer 23 b are in contact with each other.

In the case where the partition wall 98 b is used as a component of thedisplay device, cured resin is preferably used for the partition wall 98b. Here, it is preferable that the partition wall 98 b do not overlapwith the portion where the formation substrate 14 and the second resinlayer 23 b are in contact with each other.

In the case where the partition wall 98 b is not used as a component ofthe display device, an uncured resin or a semi-cured resin is preferablyused for the partition wall 98 b. Here, the partition wall 98 b mayoverlap with the portion where the formation substrate 14 and the secondresin layer 23 b are in contact with each other.

This embodiment shows an example where an uncured resin is used for thepartition wall 98 b, and the partition wall 98 b overlaps with a portionwhere the formation substrate 14 is in contact with the second resinlayer 23 b.

Thus, as illustrated in FIG. 19A, at least one place of a region wherethe first resin layer 23 a and the bonding layer 13 overlap with eachother is irradiated with the laser light 66, whereby the separationstarting point can be formed.

Then, the formation substrate 14 and the first resin layer 23 a can beseparated from each other (FIG. 19B).

Structure Example 2 of Display Device

FIG. 20A is a top view of a display device 10B. FIG. 20B is an exampleof a cross-sectional view illustrating the display portion 381 of thedisplay device 10B and a portion for connection to the FPC 372.

The display device 10B can be manufactured with the use of the abovemanufacturing method example 5. The display device 10B can be held in abent state and can be bent repeatedly, for example.

The display device 10B includes the substrate 22 and the substrate 29.The substrate 22 side is the display surface side of the display device10B. The display device 10B includes the display portion 381 and thedriver circuit portion 382. The FPC 372 is attached to the displaydevice 10B.

A conductive layer 86 c and the FPC 372 are electrically connectedthrough the connector 76 (FIG. 20B). The conductive layer 86 c can beformed using the same material and the same step as those of the sourceand the drain of the transistor.

As described above, the heat treatment performed in an oxygen-containingatmosphere enables the first resin layer to be separated from theformation substrate without laser irradiation of the entire area of thefirst resin layer. Thus, a large amount of oxygen is sometimes observedby analysis in the first resin layer of the display device that ismanufactured by the manufacturing method of a display device describedin this embodiment. Specifically, the oxygen concentration can beobtained by analyzing the surface of the first resin layer on theseparation surface side by XPS. The oxygen concentration that isobtained by analyzing the surface of the first resin layer 23 a on thebonding layer 28 side by XPS is preferably higher than or equal to 10atomic %, further preferably higher than or equal to 15 atomic %. Theoxygen concentration that is obtained by analyzing the surface of thefirst resin layer 93 a on the bonding layer 13 side by XPS is preferablyhigher than or equal to 10 atomic %, further preferably higher than orequal to 15 atomic %.

As described above, in the separation method of this embodiment, theseparability of the resin layer with respect to the formation substrateis controlled by heat conditions used to form the resin layer. Treatmentthat uses an expensive apparatus, such as linear laser beam irradiation,is not necessary for the separation method; accordingly, the costs canbe reduced. Moreover, use of a stack of two resin layers differing inseparability with respect to the formation substrate enables separationof the formation substrate and the resin layer from each other to occurat a desired time. Thus, by the separation method of this embodiment,display devices and the like can be manufactured at low cost with highmass productivity.

This embodiment can be combined with any of other embodiments asappropriate.

Embodiment 2

In this embodiment, a separation method of one embodiment of the presentinvention and a method for manufacturing a display device are describedwith reference to FIGS. 21A to 21E and FIGS. 22A1, 22A2, and 22B.

In this embodiment, the case where low-temperature polysilicon (LTPS) isused for a channel region of the transistor is described.

In the case where LTPS is used, a first resin layer and a second resinlayer are preferably thick films formed using a material having highheat resistance. Thus, a high-temperature process becomes possible anddamage in a step for laser crystallization can be reduced.

First, the first layer 24 a is formed over the formation substrate 14(FIG. 21A).

For the material and the formation method of the first layer 24 a,Embodiment 1 can be referred to. It is preferable that the heatresistance of the material of the first layer 24 a used in thisembodiment be sufficiently high.

Next, a first heat treatment is performed on the first layer 24 a havinga desired shape, whereby the first resin layer 23 a is formed (FIG.21B). Here, the first resin layer 23 a having an island shape is formed.

The first heat treatment is performed in an atmosphere containingoxygen.

Conditions of the first heat treatment can be referred to thedescription in Embodiment 1.

In this embodiment, since a material having high heat resistance is usedfor the first layer 24 a, the first heat treatment can be performed at atemperature higher than the heating temperature in Embodiment 1. Forexample, the temperature of the first heat treatment is preferablygreater than or equal to 400° C. and less than or equal to 600° C.,further preferably greater than or equal to 450° C. and less than orequal to 550° C.

The thickness of the first resin layer 23 a is preferably greater thanor equal to 10 μm and less than or equal to 200 μm, further preferablygreater than or equal to 10 μm and less than or equal to 100 μm, andstill further preferably greater than or equal to 10 μm and less than orequal to 50 μm. When the thickness of the first resin layer 23 a issufficiently large, damage in a step of laser crystallization can bereduced.

The 5% weight loss temperature of the first resin layer 23 a ispreferably greater than or equal to 400° C. and less than or equal to600° C., further preferably greater than or equal to 450° C. and lessthan or equal to 600° C., and still further preferably greater than orequal to 500° C. and less than or equal to 600° C.

Then, a second layer 24 b is formed over the formation substrate 14 andthe first resin layer 23 a (FIG. 21C).

The second layer 24 b can be formed using a material and a method thatcan be used to form the first layer 24 a. In particular, it ispreferable that the heat resistance of the material of the second layer24 b used in this embodiment be sufficiently high.

Subsequently, the second heat treatment is performed on the second resinlayer 24 b, so that the second resin layer 23 b is formed (FIG. 21D).

The second heat treatment is performed in an atmosphere containing lessoxygen than an atmosphere of the first heat treatment.

Conditions of the second heat treatment can be referred to thedescription in Embodiment 1.

In this embodiment, since a material having high heat resistance is usedfor the second layer 24 b, the second heat treatment can be performed ata temperature higher than the heating temperature in Embodiment 1. Forexample, the temperature of the second heat treatment is preferablygreater than or equal to 400° C. and less than or equal to 600° C.,further preferably greater than or equal to 450° C. and less than orequal to 550° C.

The thickness of the second resin layer 23 b is preferably greater thanor equal to 10 μm and less than or equal to 200 μm, further preferablygreater than or equal to 10 μm and less than or equal to 100 μm, stillfurther preferably greater than or equal to 10 μm and less than or equalto 50 μm. When the thickness of the second resin layer 23 b issufficiently large, damage in a step of laser crystallization can bereduced.

In the case where the thickness of one of the first resin layer 23 a andthe second resin layer 23 b is sufficiently large (e.g., greater than orequal to 20 μm), the thickness of the other may be less than 10 μm.

The 5% weight loss temperature of the second resin layer 23 b ispreferably greater than or equal to 400° C. and less than or equal to600° C., further preferably greater than or equal to 450° C. and lessthan or equal to 600° C., and still further preferably greater than orequal to 500° C. and less than or equal to 600° C.

The first resin layer 23 a and the second resin layer 23 b may be formedusing different materials or the same material. The same material ispreferably used because the cost can be reduced. Even when the samematerial is used, the degree of adhesion between the formation substrate14 and the first resin layer 23 a can be made different from thatbetween the formation substrate 14 and the second resin layer 23 b byperforming the first treatment and the second heat treatment underdifferent conditions.

Next, the insulating layer 31 is formed over the second resin layer 23 b(FIG. 21E).

The insulating layer 31 is formed at a temperature lower than or equalto the heat resistance temperature of the first resin layer 23 a andlower than or equal to the heat resistance temperature of the secondresin layer 23 b. The insulating layer 31 is preferably formed at atemperature lower than or equal to the temperature of the first heattreatment and lower than or equal to the temperature of the second heattreatment and may be formed at a temperature lower than both of thetemperature of the first heat treatment and the temperature of thesecond heat treatment.

The insulating layer 31 can be used as a barrier layer that preventsdiffusion of impurities contained in the first resin layer 23 a and thesecond resin layer 23 b into a transistor and a display element formedlater. For example, the insulating layer 31 preferably prevents moistureand the like contained in the first resin layer 23 a and the secondresin layer 23 b from diffusing into the transistor and the displayelement when the first resin layer 23 a and the second resin layer 23 bare heated. Thus, the insulating layer 31 preferably has a high barrierproperty.

For the insulating layer 31, any of the materials described inEmbodiment 1 can be used.

Next, the transistor 90 is formed over the insulating layer 31 (FIG.21E).

Here, the case where a top-gate transistor including LTPS in a channelformation region is formed as the transistor 90 is shown.

First, a semiconductor film is formed over the insulating layer 31 by asputtering method, a CVD method, or the like. In this embodiment, a50-nm-thick amorphous silicon film is formed with a plasma CVDapparatus.

Next, heat treatment is preferably performed on the amorphous siliconfilm. Thus, hydrogen can be released from the amorphous silicon film.Specifically, the amorphous silicon film is preferably heated at atemperature higher than or equal to 400° C. and less than or equal to550° C. For example, when the amount of hydrogen contained in theamorphous silicon film is smaller than or equal to 5 atomic %,manufacturing yield in the crystallization step can be improved. Theheat treatment may be omitted in the case where the amount of hydrogencontained in the amorphous silicon film is small.

In this embodiment, since the first resin layer 23 a and the secondresin layer 23 b have high heat resistance, heat treatment can beperformed at a high temperature to sufficiently release hydrogen fromthe amorphous silicon film.

Next, the semiconductor film is crystallized to form a semiconductorhaving a crystalline structure.

The semiconductor film can be crystallized by irradiation with a laserlight from above the semiconductor film. The laser light with awavelength of 193 nm, 248 nm, 308 nm, or 351 nm, for example, can beused. Alternatively, the semiconductor film may be crystallized by usinga metal catalyst element.

In this embodiment, since the first resin layer 23 a and the secondresin layer 23 b are formed to be thick, damage due to crystallizationcan be reduced.

Next, channel doping may be performed on the semiconductor film having acrystalline structure.

Next, the semiconductor film is processed to form an island-shapedsemiconductor film.

The semiconductor film can be processed by a wet etching method and/or adry etching method.

Next, the insulating layer 84 and the conductive layer 85 are formedover the insulating layer 31 and the semiconductor film. For theinsulating layer 84, the description of the inorganic insulating filmthat can be used for the insulating layer 31 can be referred to. Theinsulating layer 84 and the conductive layer 85 can be formed in thefollowing manner: an insulating film to be the insulating layer 84 isformed, a conductive film to be the conductive layer 85 is formed, amask is formed, the insulating film and the conductive film are etched,and the mask is removed.

An impurity element is added to part of the semiconductor film, wherebya channel region 83 a and low-resistance regions 83 c (also referred toas a source region and a drain region) are formed. The impurity elementmay be added plural times to form lightly doped drain (LDD) regions 83b. The insulating layer 84, the conductive layer 85, and a mask forforming these layers can function as a mask for adding impurityelements.

In the case of forming an n-channel transistor, an impurity elementimparting n-type conductivity to a semiconductor film is used. Forexample, an element such as P, As, Sb, S, Te, or Se can be used.

In the case of forming a p-channel transistor, an impurity elementimparting p-type conductivity to a semiconductor film is used. Forexample, an element such as B, Al, or Ga can be used.

Next, the insulating layer 33 that covers the semiconductor layer, theinsulating layer 84, and the conductive layer 85 is formed. Theinsulating layer 33 can be formed in a manner similar to that of theinsulating layer 31.

Next, heat treatment is performed. Thus, the impurity element which isadded to the semiconductor layer is activated. The heat treatment ispreferably performed after the formation of the insulating layer 33 soas to prevent oxidation of the conductive layer 85.

In this embodiment, since the heat resistance of the first resin layer23 a and the second resin layer 23 b is high, heat treatment foractivating the impurity element can be performed at a high temperature.Thus, the characteristics of the transistor can be improved.

The insulating layer 33 may include an insulating film containinghydrogen. When heat treatment is performed after the insulating filmcontaining hydrogen is formed over the transistor 90, hydrogen issupplied from the insulating film containing hydrogen to thesemiconductor layer (especially to the channel region 83 a); thus,defects in the semiconductor layer can be terminated with hydrogen. Theheat treatment is performed at a temperature lower than the temperatureof the heat treatment which is performed on the amorphous silicon filmin order to release hydrogen.

In this embodiment, since heat resistance of the first resin layer 23 aand the second resin layer 23 b is high, heat treatment forhydrogenation can be performed at a high temperature.

Thus, the characteristics of the transistor can be improved.

Next, openings reaching the low-resistance regions 83 c of thesemiconductor layer are formed in the insulating layer 33.

Then, the conductive layer 86 a and the conductive layer 86 b areformed. The conductive layers 86 a and 86 b can be formed in thefollowing manner: a conductive film is formed, a resist mask is formed,the conductive film is etched, and the resist mask is removed. Theconductive layers 86 a and 86 b are electrically connected to thelow-resistance regions 83 c through the openings formed in theinsulating layer 33.

In the above manner, the transistor 90 can be fabricated (FIG. 21E). Inthe transistor 90, part of the conductive layer 85 functions as a gateand part of the insulating layer 84 functions as a gate insulatinglayer. The semiconductor layer includes the channel region 83 a, the LDDregions 83 b, and the low-resistance regions 83 c. The channel region 83a overlaps with the conductive layer 85 with the insulating layer 84provided therebetween. The low-resistance regions 83 c include a regionconnected to the conductive layer 86 a and a region connected to theconductive layer 86 b.

Next, constituents from the insulating layer 34 to the protective layer75 are formed over the insulating layer 33 (see FIG. 22A1). For thesesteps, Embodiment 1 can be referred to.

Then, the separation starting point is formed in the first resin layer23 a (FIGS. 22A1 and 22A2).

For example, a sharp instrument 65 such as a knife is inserted from theprotective layer 75 side into a portion inward from an end portion ofthe first resin layer 23 a to form a frame-like-shaped cut 64.

In this embodiment, a portion that is in contact with the first resinlayer 23 a and a portion that is in contact with the second resin layer23 b are provided for the formation substrate 14. Thus, separation ofthe first resin layer 23 a from the formation substrate 14 that willoccur at an unintended time can be inhibited. Furthermore, theseparation starting point enables separation of the formation substrate14 and the first resin layer 23 a from each other at a desired time. Asa result, the time at which the separation occurs can be controlled andhigh separability can be achieved. This can improve the yield of theseparation process and the manufacturing process of the display device.

Next, the formation substrate 14 and the transistor 90 are separatedfrom each other (FIG. 22B).

The first heat treatment is performed in the atmosphere containingoxygen at the time of forming the first resin layer 23 a; thus, theformation substrate 14 and the first resin layer 23 a can be separatedfrom each other without performing laser irradiation on the entiresurface of the first resin layer 23 a. Consequently, the display devicecan be manufactured at low cost.

As described above, the first resin layer and the second resin layer areformed to be thick using a high heat-resistant material, whereby adisplay device including LTPS in a transistor can be manufactured.

This embodiment can be combined with any of other embodiments asappropriate.

Embodiment 3

In this embodiment, a display device of one embodiment of the presentinvention and a manufacturing method thereof will be described withreference to drawings.

The display device of this embodiment includes a first display elementreflecting visible light and a second display element emitting visiblelight.

The display device of this embodiment has a function of displaying animage using one or both of light reflected by the first display elementand light emitted from the second display element.

As the first display element, an element which displays an image byreflecting external light can be used. Such an element does not includea light source (or does not require an artificial light source); thus,power consumed in displaying an image can be significantly reduced.

As a typical example of the first display element, a reflective liquidcrystal element can be given. As the first display element, an elementusing a microcapsule method, an electrophoretic method, anelectrowetting method, an Electronic Liquid Powder (registeredtrademark) method, or the like can also be used, other than microelectro mechanical systems (MEMS) shutter element or an opticalinterference type MEMS element.

As the second display element, a light-emitting element is preferablyused. Since the luminance and the chromaticity of light emitted fromsuch a display element are not affected by external light, a clear imagethat has high color reproducibility (wide color gamut) and a highcontrast can be displayed.

As the second display element, a self-luminous light-emitting elementsuch as an organic light-emitting diode (OLED), a light-emitting diode(LED), or a quantum-dot light-emitting diode (QLED) can be used.

The display device of this embodiment has a first mode in which an imageis displayed using only the first display element, a second mode inwhich an image is displayed using only the second display element, and athird mode in which an image is displayed using both the first displayelement and the second display element. The display device of thisembodiment can be switched between these modes automatically ormanually.

In the first mode, an image is displayed using the first display elementand external light. Because a light source is unnecessary in the firstmode, power consumed in this mode is extremely low. When sufficientexternal light enters the display device (e.g., in a brightenvironment), for example, an image can be displayed by using lightreflected by the first display element. The first mode is effective inthe case where external light is white light or light near white lightand is sufficiently strong, for example. The first mode is suitable fordisplaying text. Furthermore, the first mode enables eye-friendlydisplay owing to the use of reflected external light, which leads to aneffect of easing eyestrain.

In the second mode, an image is displayed using light emitted from thesecond display element. Thus, an extremely vivid image (with highcontrast and excellent color reproducibility) can be displayedregardless of the illuminance and the chromaticity of external light.The second mode is effective in the case of extremely low illuminance,such as in a night environment or in a dark room, for example. When abright image is displayed in a dark environment, a user may feel thatthe image is too bright. To prevent this, an image with reducedluminance is preferably displayed in the second mode. In that case,glare can be reduced, and power consumption can also be reduced. Thesecond mode is suitable for displaying a vivid (still and moving) imageor the like.

In the third mode, an image is displayed using both light reflected bythe first display element and light emitted from the second displayelement. An image displayed in the third mode can be more vivid than animage displayed in the first mode while power consumption can be lowerthan that in the second mode. The third mode is effective in the casewhere the illuminance is relatively low or in the case where thechromaticity of external light is not white, for example, in anenvironment under indoor illumination or in the morning or evening.

With such a structure, an all-weather display device or a highlyconvenient display device with high visibility regardless of the ambientbrightness can be fabricated.

The display device of this embodiment includes a plurality of firstpixels including the first display elements and a plurality of secondpixels including the second display elements. The first pixels and thesecond pixels are preferably arranged in matrices.

Each of the first pixels and the second pixels can include one or moresub-pixels. For example, each pixel can include one sub-pixel (e.g., awhite (W) sub-pixel), three sub-pixels (e.g., red (R), green (G), andblue (B) sub-pixels, or yellow (Y), cyan (C), and magenta (M)sub-pixels), or four sub-pixels (e.g., red (R), green (G), blue (B), andwhite (W) sub-pixels, or red (R), green (G), blue (B), and yellow (Y)sub-pixels).

The display device of this embodiment can display a full-color imageusing either the first pixels or the second pixels. Alternatively, thedisplay device of this embodiment can display a black-and-white image ora grayscale image using the first pixels and can display a full-colorimage using the second pixels. The first pixels that can be used fordisplaying a black-and-white image or a grayscale image are suitable fordisplaying information that need not be displayed in color such as textinformation.

Structure examples of the display device in this embodiment aredescribed with reference to FIG. 23, FIG. 24, FIG. 25, and FIG. 26.

Structure Example 1

FIG. 23 is a schematic perspective view of a display device 300. In thedisplay device 300, the substrate 351 and the substrate 361 are bondedto each other. In FIG. 23, the substrate 361 is denoted by a dashedline.

The display device 300 includes a display portion 362, a circuit 364, awiring 365, and the like. FIG. 23 illustrates an example in which thedisplay device 300 is provided with an integrated circuit (IC) 373 andan FPC 372. Thus, the structure illustrated in FIG. 23 can be regardedas a display module including the display device 300, the IC, and theFPC.

As the circuit 364, for example, a scan line driver circuit can be used.

The wiring 365 has a function of supplying a signal and power to thedisplay portion 362 and the circuit 364. The signal and power are inputto the wiring 365 from the outside through the FPC 372 or from the IC373.

FIG. 23 illustrates an example in which the IC 373 is provided over thesubstrate 351 by a chip on glass (COG) method, a chip on film (COF)method, or the like. An IC including a scan line driver circuit, asignal line driver circuit, or the like can be used as the IC 373, forexample. Note that the display device 300 and the display module are notnecessarily provided with an IC. The IC may be provided over the FPC bya COF method or the like.

FIG. 23 illustrates an enlarged view of part of the display portion 362.Electrodes 311 b included in a plurality of display elements arearranged in a matrix in the display portion 362. The electrode 311 b hasa function of reflecting visible light, and serves as a reflectiveelectrode of the liquid crystal element 180.

As illustrated in FIG. 23, the electrode 311 b includes an opening 451.In addition, the display portion 362 includes the light-emitting element170 that is positioned closer to the substrate 351 than the electrode311 b. Light from the light-emitting element 170 is emitted to thesubstrate 361 side through the opening 451 in the electrode 311 b. Thearea of the light-emitting region of the light-emitting element 170 maybe equal to the area of the opening 451. One of the area of thelight-emitting region of the light-emitting element 170 and the area ofthe opening 451 is preferably larger than the other because a margin formisalignment can be increased. It is particularly preferable that thearea of the opening 451 be larger than the area of the light-emittingregion of the light-emitting element 170. When the area of the opening451 is small, part of light from the light-emitting element 170 isblocked by the electrode 311 b and cannot be extracted to the outside,in some cases. The opening 451 with a sufficiently large area can reducewaste of light emitted from the light-emitting element 170.

FIG. 24 illustrates an example of cross-sections of part of a regionincluding the FPC 372, part of a region including the circuit 364, andpart of a region including the display portion 362 of the display device300 illustrated in FIG. 23.

The display device 300 illustrated in FIG. 24 includes a transistor 201,a transistor 203, a transistor 205, a transistor 206, the liquid crystalelement 180, the light-emitting element 170, an insulating layer 220, acoloring layer 131, a coloring layer 134, and the like, between thesubstrate 351 and the substrate 361. The substrate 361 and theinsulating layer 220 are bonded to each other with a bonding layer 141.The substrate 351 and the insulating layer 220 are bonded to each otherwith a bonding layer 142.

The substrate 361 is provided with the coloring layer 131, alight-blocking layer 132, an insulating layer 121, an electrode 113functioning as a common electrode of the liquid crystal element 180, analignment film 133 b, an insulating layer 117, and the like. Apolarizing plate 135 is provided on an outer surface of the substrate361. The insulating layer 121 may have a function of a planarizationlayer. The insulating layer 121 enables the electrode 113 to have analmost flat surface, resulting in a uniform alignment state of a liquidcrystal layer 112. The insulating layer 117 serves as a spacer forholding a cell gap of the liquid crystal element 180. In the case wherethe insulating layer 117 transmits visible light, the insulating layer117 may be positioned to overlap with a display region of the liquidcrystal element 180.

The liquid crystal element 180 is a reflective liquid crystal element.The liquid crystal element 180 has a stacked-layer structure of anelectrode 311 a serving as a pixel electrode, the liquid crystal layer112, and the electrode 113. The electrode 311 b that reflects visiblelight is provided in contact with a surface of the electrode 311 a onthe substrate 351 side. The electrode 311 b includes the opening 451.The electrode 311 a and the electrode 113 transmit visible light. Analignment film 133 a is provided between the liquid crystal layer 112and the electrode 311 a. The alignment film 133 b is provided betweenthe liquid crystal layer 112 and the electrode 113.

In the liquid crystal element 180, the electrode 311 b has a function ofreflecting visible light, and the electrode 113 has a function oftransmitting visible light. Light entering from the substrate 361 sideis polarized by the polarizing plate 135, transmitted through theelectrode 113 and the liquid crystal layer 112, and reflected by theelectrode 311 b. Then, the light is transmitted through the liquidcrystal layer 112 and the electrode 113 again to reach the polarizingplate 135. In this case, alignment of a liquid crystal can be controlledwith a voltage that is applied between the electrode 311 b and theelectrode 113, and thus optical modulation of light can be controlled.In other words, the intensity of light emitted through the polarizingplate 135 can be controlled. Light excluding light in a particularwavelength region is absorbed by the coloring layer 131 and thus,emitted light is red light, for example.

As illustrated in FIG. 24, the electrode 311 a that transmits visiblelight is preferably provided across the opening 451. Accordingly, liquidcrystals in the liquid crystal layer 112 are aligned in a regionoverlapping with the opening 451 as in the other regions, in which casean alignment defect of the liquid crystals in a boundary portion ofthese regions is prevented and undesired light leakage can besuppressed.

At a connection portion 207, the electrode 311 b is electricallyconnected to a conductive layer 222 a included in the transistor 206 viaa conductive layer 221 b. The transistor 206 has a function ofcontrolling the driving of the liquid crystal element 180.

A connection portion 252 is provided in part of a region where thebonding layer 141 is provided. In the connection portion 252, aconductive layer obtained by processing the same conductive film as theelectrode 311 a is electrically connected to part of the electrode 113with a connector 243. Accordingly, a signal or a potential input fromthe FPC 372 connected to the substrate 351 side can be supplied to theelectrode 113 formed on the substrate 361 side through the connectionportion 252.

As the connector 243, for example, a conductive particle can be used. Asthe conductive particle, a particle of an organic resin, silica, or thelike coated with a metal material can be used. It is preferable to usenickel or gold as the metal material because contact resistance can bedecreased. It is also preferable to use a particle coated with layers oftwo or more kinds of metal materials, such as a particle coated withnickel and further with gold. A material capable of elastic deformationor plastic deformation is preferably used for the connector 243. Asillustrated in FIG. 24, the connector 243, which is the conductiveparticle, has a shape that is vertically crushed in some cases. With thecrushed shape, the contact area between the connector 243 and aconductive layer electrically connected to the connector 243 can beincreased, thereby reducing contact resistance and suppressing thegeneration of problems such as disconnection.

The connector 243 is preferably provided so as to be covered with thebonding layer 141. For example, the connectors 243 are dispersed in thebonding layer 141 before curing of the bonding layer 141.

The light-emitting element 170 is a bottom-emission light-emittingelement. The light-emitting element 170 has a stacked-layer structure inwhich an electrode 191 serving as a pixel electrode, an EL layer 192,and an electrode 193 serving as a common electrode are stacked in thisorder from the insulating layer 220 side. The electrode 191 is connectedto the conductive layer 222 a included in the transistor 205 through anopening provided in an insulating layer 214. The transistor 205 has afunction of controlling the driving of the light-emitting element 170.An insulating layer 216 covers an end portion of the electrode 191. Theelectrode 193 includes a material that reflects visible light, and theelectrode 191 includes a material that transmits visible light. Aninsulating layer 194 is provided to cover the electrode 193. Light isemitted from the light-emitting element 170 to the substrate 361 sidethrough the coloring layer 134, the insulating layer 220, the opening451, the electrode 311 a, and the like.

The liquid crystal element 180 and the light-emitting element 170 canexhibit various colors when the color of the coloring layer varies amongpixels. The display device 300 can display a color image using theliquid crystal element 180. The display device 300 can display a colorimage using the light-emitting element 170.

The transistor 201, the transistor 203, the transistor 205, and thetransistor 206 are formed on a plane of the insulating layer 220 on thesubstrate 351 side. These transistors can be fabricated through the sameprocess.

A circuit electrically connected to the liquid crystal element 180 and acircuit electrically connected to the light-emitting element 170 arepreferably formed on the same plane. In that case, the thickness of thedisplay device can be smaller than that in the case where the twocircuits are formed on different planes. Furthermore, since twotransistors can be formed in the same process, a manufacturing processcan be simplified as compared to the case where two transistors areformed on different planes.

The pixel electrode of the liquid crystal element 180 is positioned onthe opposite side of a gate insulating layer included in the transistorfrom the pixel electrode of the light-emitting element 170.

In the case where a transistor including a metal oxide in its channelformation region and having an extremely low off-state current is usedas the transistor 206 or in the case where a memory element electricallyconnected to the transistor 206 is used, for example, in displaying astill image using the liquid crystal element 180, even if writingoperation to a pixel is stopped, the gray level can be maintained. Inother words, an image can be kept displayed even with an extremely lowframe rate. In one embodiment of the present invention, the frame ratecan be extremely low and driving with low power consumption can beperformed.

The transistor 203 is used for controlling whether the pixel is selectedor not (such a transistor is also referred to as a switching transistoror a selection transistor). The transistor 205 is used for controllingcurrent flowing to the light-emitting element 170 (such a transistor isalso referred to as a driving transistor).

Insulating layers such as an insulating layer 211, an insulating layer212, an insulating layer 213, and the insulating layer 214 are providedon the substrate 351 side of the insulating layer 220. Part of theinsulating layer 211 functions as a gate insulating layer of eachtransistor. The insulating layer 212 is provided to cover the transistor206 and the like. The insulating layer 213 is provided to cover thetransistor 205 and the like. The insulating layer 214 functions as aplanarization layer. Note that the number of insulating layers coveringthe transistor is not limited and may be one or two or more.

A material through which impurities such as water or hydrogen do noteasily diffuse is preferably used for at least one of the insulatinglayers that cover the transistors. This is because such an insulatinglayer can serve as a barrier film. Such a structure can effectivelysuppress diffusion of the impurities into the transistors from theoutside, and a highly reliable display device can be provided.

Each of the transistors 201, 203, 205, and 206 includes a conductivelayer 221 a functioning as a gate, the insulating layer 211 functioningas the gate insulating layer, the conductive layer 222 a and aconductive layer 222 b functioning as a source and a drain, and asemiconductor layer 231. Here, a plurality of layers obtained byprocessing the same conductive film are shown with the same hatchingpattern.

The transistor 201 and the transistor 205 each include a conductivelayer 223 functioning as a gate, in addition to the components of thetransistor 203 or the transistor 206.

The structure in which the semiconductor layer where a channel is formedis provided between two gates is used as an example of the transistors201 and 205. Such a structure enables the control of the thresholdvoltages of transistors. The two gates may be connected to each otherand supplied with the same signal to operate the transistors. Suchtransistors can have higher field-effect mobility and thus have a higheron-state current than other transistors. Consequently, a circuit capableof high-speed operation can be obtained. Furthermore, the area occupiedby a circuit portion can be reduced. The use of the transistor having ahigh on-state current can reduce signal delay in wirings and can reducedisplay unevenness even in a display device in which the number ofwirings is increased because of an increase in size or resolution.

Alternatively, by supplying a potential for controlling the thresholdvoltage to one of the two gates and a potential for driving to theother, the threshold voltage of the transistor can be controlled.

There is no limitation on the structure of the transistors included inthe display device. The transistor included in the circuit 364 and thetransistor included in the display portion 362 may have the samestructure or different structures. A plurality of transistors includedin the circuit 364 may have the same structure or a combination of twoor more kinds of structures. Similarly, a plurality of transistorsincluded in the display portion 362 may have the same structure or acombination of two or more kinds of structures.

It is preferable to use a conductive material containing an oxide forthe conductive layer 223. A conductive film used for the conductivelayer 223 is formed in an oxygen-containing atmosphere, whereby oxygencan be supplied to the insulating layer 212. The proportion of an oxygengas in a deposition gas is preferably higher than or equal to 90% andlower than or equal to 100%. Oxygen supplied to the insulating layer 212is then supplied to the semiconductor layer 231 by later heat treatment;as a result, oxygen vacancies in the semiconductor layer 231 can bereduced.

It is particularly preferable to use a low-resistance metal oxide forthe conductive layer 223. In that case, an insulating film that releaseshydrogen, such as a silicon nitride film, is preferably used for theinsulating layer 213, for example, because hydrogen can be supplied tothe conductive layer 223 during the formation of the insulating layer213 or by heat treatment performed after the formation of the insulatinglayer 213, which leads to an effective reduction in the electricresistance of the conductive layer 223.

The coloring layer 134 is provided in contact with the insulating layer213. The coloring layer 134 is covered with the insulating layer 214.

A connection portion 204 is provided in a region where the substrate 351does not overlap with the substrate 361. In the connection portion 204,the wiring 365 is electrically connected to the FPC 372 via a connectionlayer 242. The connection portion 204 has a structure similar to that ofthe connection portion 207. On the top surface of the connection portion204, a conductive layer obtained by processing the same conductive filmas the electrode 311 a is exposed. Thus, the connection portion 204 andthe FPC 372 can be electrically connected to each other via theconnection layer 242.

As the polarizing plate 135 provided on the outer surface of thesubstrate 361, a linear polarizing plate or a circularly polarizingplate can be used. An example of a circularly polarizing plate is astack including a linear polarizing plate and a quarter-wave retardationplate. Such a structure can reduce reflection of external light. Thecell gap, alignment, drive voltage, and the like of the liquid crystalelement used as the liquid crystal element 180 are controlled dependingon the kind of the polarizing plate so that desirable contrast isobtained.

Note that a variety of optical members can be arranged on the outersurface of the substrate 361. Examples of the optical members include apolarizing plate, a retardation plate, a light diffusion layer (e.g., adiffusion film), an anti-reflective layer, and a light-condensing film.Furthermore, an antistatic film preventing the attachment of dust, awater repellent film suppressing the attachment of stain, a hard coatfilm suppressing generation of a scratch caused by the use, or the likemay be arranged on the outer surface of the substrate 361.

For each of the substrates 351 and 361, glass, quartz, ceramic,sapphire, an organic resin, or the like can be used. When the substrates351 and 361 are formed using a flexible material, the flexibility of thedisplay device can be increased.

A liquid crystal element having, for example, a vertical alignment (VA)mode can be used as the liquid crystal element 180. Examples of thevertical alignment mode include a multi-domain vertical alignment (MVA)mode, a patterned vertical alignment (PVA) mode, and an advanced superview (ASV) mode.

A liquid crystal element having a variety of modes can be used as theliquid crystal element 180. For example, a liquid crystal element using,instead of a VA mode, a twisted nematic (TN) mode, an in-plane switching(IPS) mode, a fringe field switching (FFS) mode, an axially symmetricaligned micro-cell (ASM) mode, an optically compensated birefringence(OCB) mode, a ferroelectric liquid crystal (FLC) mode, anantiferroelectric liquid crystal (AFLC) mode, or the like can be used.

The liquid crystal element is an element that controls transmission ornon-transmission of light utilizing an optical modulation action of theliquid crystal. The optical modulation action of the liquid crystal iscontrolled by an electric field applied to the liquid crystal (includinga horizontal electric field, a vertical electric field, and an obliqueelectric field). As the liquid crystal used for the liquid crystalelement, a thermotropic liquid crystal, a low-molecular liquid crystal,a high-molecular liquid crystal, a polymer dispersed liquid crystal(PDLC), a ferroelectric liquid crystal, an anti-ferroelectric liquidcrystal, or the like can be used. Such a liquid crystal materialexhibits a cholesteric phase, a smectic phase, a cubic phase, a chiralnematic phase, an isotropic phase, or the like depending on conditions.

As the liquid crystal material, a positive liquid crystal or a negativeliquid crystal may be used, and an appropriate liquid crystal materialcan be used depending on the mode or design to be used.

To control the alignment of the liquid crystal, the alignment films canbe provided. In the case where a horizontal electric field mode isemployed, a liquid crystal exhibiting a blue phase for which analignment film is unnecessary may be used. The blue phase is one ofliquid crystal phases, which is generated just before a cholestericphase changes into an isotropic phase while the temperature of acholesteric liquid crystal is increased. Since the blue phase appearsonly in a narrow temperature range, a liquid crystal composition inwhich several weight percent or more of a chiral material is mixed isused for the liquid crystal in order to improve the temperature range.The liquid crystal composition that includes a liquid crystal exhibitinga blue phase and a chiral material has a short response time and hasoptical isotropy. In addition, the liquid crystal composition thatincludes a liquid crystal exhibiting a blue phase and a chiral materialdoes not need alignment treatment and has small viewing angledependence. An alignment film does not need to be provided and rubbingtreatment is thus not necessary; accordingly, electrostatic dischargedamage caused by the rubbing treatment can be prevented and defects anddamage of a liquid crystal display device in the manufacturing processcan be reduced.

In the case where the reflective liquid crystal element is used, thepolarizing plate 135 is provided on the display surface side. Inaddition, a light diffusion plate is preferably provided on the displaysurface side to improve visibility.

A front light may be provided on the outer side of the polarizing plate135. As the front light, an edge-light front light is preferably used. Afront light including an LED is preferably used to reduce powerconsumption.

For the materials that can be used for the light-emitting element, thetransistors, the insulating layers, the conductive layers, the adhesivelayers, the connection layer, and the like, the description inEmbodiment 1 can be referred to.

Structure Example 2

A display device 300A illustrated in FIG. 25 is different from thedisplay device 300 mainly in that a transistor 281, a transistor 284, atransistor 285, and a transistor 286 are included instead of thetransistor 201, the transistor 203, the transistor 205, and thetransistor 206.

Note that the positions of the insulating layer 117, the connectionportion 207, and the like in FIG. 25 are different from those in FIG.24. FIG. 25 illustrates an end portion of a pixel. The insulating layer117 is provided so as to overlap with an end portion of the coloringlayer 131 and an end portion of the light-blocking layer 132. As in thisstructure, the insulating layer 117 may be provided in a region notoverlapping with a display region (or in a region overlapping with thelight-blocking layer 132).

Two transistors included in the display device may partly overlap witheach other like the transistor 284 and the transistor 285. In that case,the area occupied by a pixel circuit can be reduced, leading to anincrease in resolution. Furthermore, the light-emitting area of thelight-emitting element 170 can be increased, leading to an improvementin aperture ratio. The light-emitting element 170 with a high apertureratio requires low current density to obtain necessary luminance; thus,the reliability is improved.

Each of the transistors 281, 284, and 286 includes the conductive layer221 a, the insulating layer 211, the semiconductor layer 231, theconductive layer 222 a, and the conductive layer 222 b. The conductivelayer 221 a overlaps with the semiconductor layer 231 with theinsulating layer 211 positioned therebetween. The conductive layer 222 aand the conductive layer 222 b are electrically connected to thesemiconductor layer 231. The transistor 281 includes the conductivelayer 223.

The transistor 285 includes the conductive layer 222 b, an insulatinglayer 217, a semiconductor layer 261, the conductive layer 223, theinsulating layer 212, the insulating layer 213, a conductive layer 263a, and a conductive layer 263 b. The conductive layer 222 b overlapswith the semiconductor layer 261 with the insulating layer 217positioned therebetween. The conductive layer 223 overlaps with thesemiconductor layer 261 with the insulating layers 212 and 213positioned therebetween. The conductive layer 263 a and the conductivelayer 263 b are electrically connected to the semiconductor layer 261.

The conductive layer 221 a functions as a gate. The insulating layer 211functions as a gate insulating layer. The conductive layer 222 afunctions as one of a source and a drain. The conductive layer 222 bincluded in the transistor 286 functions as the other of the source andthe drain.

The conductive layer 222 b shared by the transistor 284 and thetransistor 285 has a portion functioning as the other of a source and adrain of the transistor 284 and a portion functioning as a gate of thetransistor 285. The insulating layer 217, the insulating layer 212, andthe insulating layer 213 function as gate insulating layers. One of theconductive layer 263 a and the conductive layer 263 b functions as asource and the other functions as a drain. The conductive layer 223functions as a gate.

Structure Example 3

FIG. 26 is a cross-sectional view illustrating a display portion of adisplay device 300B.

The display device 300B illustrated in FIG. 26 includes the transistor40, the transistor 80, the liquid crystal element 180, thelight-emitting element 170, the insulating layer 220, the coloring layer131, the coloring layer 134, and the like, between the substrate 351 andthe substrate 361.

For the structures and manufacturing methods of the transistor 40 andthe transistor 80, Embodiment 1 can be referred to.

In the liquid crystal element 180, external light is reflected on theelectrode 311 b and emitted to the substrate 361 side. Thelight-emitting element 170 emits light to the substrate 361 side. Forthe structures of the liquid crystal element 180 and the light-emittingelement 170, the structure example 1 can be referred to.

The substrate 361 is provided with the coloring layer 131, theinsulating layer 121, the electrode 113 functioning as the commonelectrode of the liquid crystal element 180, the alignment film 133 b.

The liquid crystal layer 112 is sandwiched between the electrode 311 aand the electrode 113 with the alignment film 133 a positioned betweenthe electrode 311 a and the liquid crystal layer 112 and with thealignment film 133 b positioned between the electrode 113 and the liquidcrystal layer 112.

The transistor 40 is covered with the insulating layer 212 and theinsulating layer 213. The insulating layer 213 and the coloring layer134 are bonded to the insulating layer 194 with the bonding layer 142.

In the display device 300B, the transistor 40 for driving the liquidcrystal element 180 and the transistor 80 for driving the light-emittingelement 170 are formed over different planes; thus, each of thetransistors can be easily formed using a structure and a materialsuitable for driving the corresponding display element.

Manufacturing Method Example of Display Device 300

Next, the manufacturing method of the display device of this embodimentwill be specifically described with reference to FIGS. 27A to 27F, FIGS.28A to 28C, FIGS. 29A and 29B, and FIGS. 30A and 30B. An example of amanufacturing method of the display device 300 illustrated in FIG. 24will be described below. The manufacturing method will be described withreference to FIGS. 27A to 27F, FIGS. 28A to 28C, FIGS. 29A and 29B, andFIGS. 30A and 30B, focusing on the display portion 362 of the displaydevice 300A. Note that the transistor 203 is not illustrated in FIGS.27A to 27F, FIGS. 28A to 28C, FIGS. 29A and 29B, and FIGS. 30A and 30B.

First, the coloring layer 131 is formed over the substrate 361 (FIG.27A). The coloring layer 131 is formed using a photosensitive material,in which case the processing into an island shape can be performed by aphotolithography method or the like. Note that in the circuit 364 andthe like illustrated in FIG. 24, the light-blocking layer 132 isprovided over the substrate 361.

Then, the insulating layer 121 is formed over the coloring layer 131 andthe light-blocking layer 132.

The insulating layer 121 preferably functions as a planarization layer.A resin such as acrylic or epoxy is suitably used for the insulatinglayer 121.

An inorganic insulating film may be used for the insulating layer 121.For example, an inorganic insulating film such as a silicon nitridefilm, a silicon oxynitride film, a silicon oxide film, a silicon nitrideoxide film, an aluminum oxide film, or an aluminum nitride film can beused for the insulating layer 121. Alternatively, a hafnium oxide film,an yttrium oxide film, a zirconium oxide film, a gallium oxide film, atantalum oxide film, a magnesium oxide film, a lanthanum oxide film, acerium oxide film, a neodymium oxide film, or the like may be used.Further alternatively, a stack including two or more of the aboveinsulating films may be used.

Next, the electrode 113 is formed. The electrode 113 can be formed inthe following manner: a conductive film is formed, a resist mask isformed, the conductive film is etched, and the resist mask is removed.The electrode 113 is formed using a conductive material that transmitsvisible light.

After that, the insulating layer 117 is formed over the electrode 113.An organic insulating film is preferably used for the insulating layer117.

Subsequently, the alignment film 133 b is formed over the electrode 113and the insulating layer 117 (FIG. 27A). The alignment film 133 b can beformed in the following manner: a thin film is formed using a resin orthe like and then, rubbing treatment is performed.

Note that steps illustrated in FIGS. 27B to 27F, FIGS. 28A to 28C, FIGS.29A and 29B, and FIGS. 30A and 30B are performed independently of thesteps described with reference to FIG. 27A.

First, the first layer 24 a is formed over the formation substrate 14 ina manner similar to that of the manufacturing method example 2 inEmbodiment 1 (FIG. 27B). Subsequently, the first heat treatment isperformed on the first layer 24 a that has been processed into a desiredshape, so that the first resin layer 23 a is formed (FIG. 27C). In theexample illustrated in FIG. 27C, the first resin layer 23 a having anisland-like shape is formed. The first heat treatment is performed in anoxygen-containing atmosphere. Then, the second layer 24 b is formed overthe formation substrate 14 and the first resin layer 23 a (FIG. 27D).Subsequently, the second heat treatment is performed on the second resinlayer 24 b, so that the second resin layer 23 b is formed (FIG. 27E).The second heat treatment is performed in an atmosphere containing lessoxygen than an atmosphere of the first heat treatment.

Next, the electrode 311 a is formed over the second resin layer 23 b,and the electrode 311 b is formed over the electrode 311 a (FIG. 27F).The electrode 311 b includes the opening 451 over the electrode 311 a.Each of the electrodes 311 a and 311 b can be formed in the followingmanner: a conductive film is formed, a resist mask is formed, theconductive film is etched, and the resist mask is removed. The electrode311 a is formed using a conductive material that transmits visiblelight. The electrode 311 b is formed using a conductive material thatreflects visible light.

The electrode 311 a may be formed over an insulating film formed overthe second resin layer 23 b. As the insulating film, an inorganicinsulating film that can be used to form the insulating layer 121 issuitably used. The insulating layer can be used as a barrier layer thatprevents diffusion of impurities contained in the first resin layer 23 aand the second resin layer 23 b into a transistor and a display elementformed later.

After that, the insulating layer 220 is formed (FIG. 28A). Then, anopening that reaches the electrode 311 b is formed in the insulatinglayer 220.

The insulating layer 220 can be used as a barrier layer that preventsdiffusion of impurities contained in the first resin layer 23 a and thesecond resin layer 23 b into a transistor and a display element formedlater. For example, the insulating layer 220 preferably preventsmoisture and the like contained in the first resin layer 23 a and thesecond resin layer 23 b from diffusing into the transistor and thedisplay element when the first resin layer 23 a and the second resinlayer 23 b is heated. Thus, the insulating layer 220 preferably has ahigh barrier property.

The insulating layer 220 can be formed using the inorganic insulatingfilm, the resin, or the like that can be used for the insulating layer121.

Next, the transistor 205 and the transistor 206 are formed over theinsulating layer 220.

There is no particular limitation on a semiconductor material used forthe semiconductor layer of the transistor, and for example, a Group 14element, a compound semiconductor, or an oxide semiconductor can beused. Typically, a semiconductor containing silicon, a semiconductorcontaining gallium arsenide, an oxide semiconductor containing indium,or the like can be used.

Described here is the case where a bottom-gate transistor including ametal oxide layer as the semiconductor layer 231 is fabricated as thetransistor 206. The transistor 205 includes the conductive layer 223 andthe insulating layer 212 in addition to the components of the transistor206, and has two gates. A metal oxide can function as an oxidesemiconductor.

Specifically, first, the conductive layer 221 a and the conductive layer221 b are formed over the insulating layer 220. The conductive layer 221a and the conductive layer 221 b can be formed in the following manner:a conductive film is formed, a resist mask is formed, the conductivefilm is etched, and the resist mask is removed. At this time, theconductive layer 221 b and the electrode 311 b are connected to eachother through an opening in the insulating layer 220.

Next, the insulating layer 211 is formed.

For the insulating layer 211, for example, an inorganic insulating filmsuch as a silicon nitride film, a silicon oxynitride film, a siliconoxide film, a silicon nitride oxide film, an aluminum oxide film, or analuminum nitride film can be used. Alternatively, a hafnium oxide film,an yttrium oxide film, a zirconium oxide film, a gallium oxide film, atantalum oxide film, a magnesium oxide film, a lanthanum oxide film, acerium oxide film, a neodymium oxide film, or the like may be used.Further alternatively, a stack including two or more of the aboveinsulating films may be used.

An inorganic insulating film is preferably formed at high temperaturesbecause the film can have higher density and a higher barrier propertyas the deposition temperature becomes higher. The substrate temperatureduring the formation of the inorganic insulating film is preferablyhigher than or equal to room temperature (25° C.) and lower than orequal to 350° C., further preferably higher than or equal to 100° C. andlower than or equal to 300° C.

Then, the semiconductor layer 231 is formed. In this embodiment, a metaloxide layer is formed as the semiconductor layer 231. The metal oxidelayer can be formed in the following manner: a metal oxide film isformed, a resist mask is formed, the metal oxide film is etched, and theresist mask is removed.

Next, the conductive layer 222 a and the conductive layer 222 b areformed. The conductive layer 222 a and the conductive layer 222 b can beformed in the following manner: a conductive film is formed, a resistmask is formed, the conductive film is etched, and the resist mask isremoved. Each of the conductive layers 222 a and 222 b is connected tothe semiconductor layer 231. Here, the conductive layer 222 a includedin the transistor 206 is electrically connected to the conductive layer221 b. As a result, the electrode 311 b and the conductive layer 222 acan be electrically connected to each other at the connection portion207.

Note that during the processing of the conductive layer 222 a and theconductive layer 222 b, the semiconductor layer 231 might be partlyetched to be thin in a region not covered by the resist mask.

In the above manner, the transistor 206 can be fabricated (FIG. 28A). Inthe transistor 206, part of the conductive layer 221 a functions as agate, part of the insulating layer 211 functions as a gate insulatinglayer, and the conductive layer 222 a and the conductive layer 222 bfunction as a source and a drain.

Next, the insulating layer 212 that covers the transistor 206 is formed.The insulating layer 212 is formed to cover the semiconductor layer 231,the conductive layer 222 a, and the conductive layer 222 b of each ofthe transistor 205 and the transistor 206. Next, the conductive layer223 of the transistor 205 is formed over the insulating layer 212.

The insulating layer 212 can be formed in a manner similar to that ofthe insulating layer 211.

The conductive layer 223 included in the transistor 205 can be formed inthe following manner: a conductive film is formed, a resist mask isformed, the conductive film is etched, and the resist mask is removed.

In the above manner, the transistor 205 can be fabricated (FIG. 28A). Inthe transistor 205, part of the conductive layer 221 a and part of theconductive layer 223 function as gates, part of the insulating layer 211and part of the insulating layer 212 function as gate insulating layers,and the conductive layer 222 a and the conductive layer 222 b functionas a source and a drain.

Next, the insulating layer 213 covering the transistor 205 and thetransistor 206 is formed (FIG. 28A). The insulating layer 213 can beformed in a manner similar to that of the insulating layer 211.

It is preferable to use an oxide insulating film formed in anoxygen-containing atmosphere, such as a silicon oxide film or a siliconoxynitride film, for the insulating layer 212. An insulating film withlow oxygen diffusibility and oxygen permeability, such as a siliconnitride film, is preferably stacked as the insulating layer 213 over thesilicon oxide film or the silicon oxynitride film. The oxide insulatingfilm formed in an oxygen-containing atmosphere can easily release alarge amount of oxygen by heating. When a stack including such an oxideinsulating film that releases oxygen and such an insulating film withlow oxygen diffusibility and oxygen permeability is heated, oxygen canbe supplied to the metal oxide layer. As a result, oxygen vacancies inthe metal oxide layer can be filled and defects at the interface betweenthe metal oxide layer and the insulating layer 212 can be repaired,leading to a reduction in defect levels. Accordingly, a display devicewith extremely high reliability can be fabricated.

Next, the coloring layer 134 is formed over the insulating layer 213(FIG. 28A) and then, the insulating layer 214 is formed (FIG. 28B). Thecoloring layer 134 is positioned so as to overlap with the opening 451in the electrode 311 b.

The coloring layer 134 can be formed in a manner similar to that of thecoloring layer 131. The display element is formed on the insulatinglayer 214 in a later step; thus, the insulating layer 214 preferablyfunctions as a planarization layer. For the insulating layer 214, thedescription of the resin or the inorganic insulating film that can beused for the insulating layer 121 can be referred to.

After that, an opening that reaches the conductive layer 222 a includedin the transistor 205 is formed in the insulating layer 212, theinsulating layer 213, and the insulating layer 214.

Subsequently, the electrode 191 is formed (FIG. 28B). The electrode 191can be formed in the following manner: a conductive film is formed, aresist mask is formed, the conductive film is etched, and the resistmask is removed. Here, the conductive layer 222 a included in thetransistor 205 and the electrode 191 are connected to each other. Theelectrode 191 is formed using a conductive material that transmitsvisible light.

Then, the insulating layer 216 that covers the end portion of theelectrode 191 is formed (FIG. 28B). For the insulating layer 216, thedescription of the resin or the inorganic insulating film that can beused for the insulating layer 121 can be referred to. The insulatinglayer 216 includes an opening in a region overlapping with the electrode191.

Next, the EL layer 192 and the electrode 193 are formed (FIG. 28B). Partof the electrode 193 functions as the common electrode of thelight-emitting element 170. The electrode 193 is formed using aconductive material that reflects visible light.

Steps after the formation of the EL layer 192 are performed such thattemperatures higher than the upper temperature limit of the EL layer 192are not applied to the EL layer 192. The electrode 193 can be formed byan evaporation method, a sputtering method, or the like.

In the above manner, the light-emitting element 170 can be formed (FIG.28B). In the light-emitting element 170, the electrode 191 part of whichfunctions as the pixel electrode, the EL layer 192, and the electrode193 part of which functions as the common electrode are stacked. Thelight-emitting element 170 is formed such that the light-emitting regionoverlaps with the coloring layer 134 and the opening 451 in theelectrode 311 b.

Next, the insulating layer 194 is formed so as to cover the electrode193 (FIG. 28B). The insulating layer 194 functions as a protective layerthat prevents diffusion of impurities such as water into thelight-emitting element 170. The light-emitting element 170 is sealedwith the insulating layer 194. After the electrode 193 is formed, theinsulating layer 194 is preferably formed without exposure to the air.

The inorganic insulating film that can be used for the insulating layer121 can be used for the insulating layer 194, for example. It isparticularly preferable that the insulating layer 194 include aninorganic insulating film with a high barrier property. A stackincluding an inorganic insulating film and an organic insulating filmcan also be used.

The insulating layer 194 is preferably formed at substrate temperaturelower than or equal to the upper temperature limit of the EL layer 192.The insulating layer 194 can be formed by an ALD method, a sputteringmethod, or the like. An ALD method and a sputtering method arepreferable because a film can be formed at low temperatures. An ALDmethod is preferable because the coverage with the insulating layer 194is improved.

Then, the substrate 351 is bonded to a surface of the insulating layer194 with the bonding layer 142 (FIG. 28C).

As the adhesive layer 142, any of a variety of curable adhesives such asa reactive curable adhesive, a thermosetting adhesive, an anaerobicadhesive, and a photocurable adhesive such as an ultraviolet curableadhesive can be used. Still alternatively, an adhesive sheet or the likemay be used.

For the substrate 351, a polyester resin such as polyethyleneterephthalate (PET) or polyethylene naphthalate (PEN), apolyacrylonitrile resin, an acrylic resin, a polyimide resin, apolymethyl methacrylate resin, a polycarbonate (PC) resin, apolyethersulfone (PES) resin, a polyamide resin (e.g., nylon or aramid),a polysiloxane resin, a cycloolefin resin, a polystyrene resin, apolyamide-imide resin, a polyurethane resin, a polyvinyl chloride resin,a polyvinylidene chloride resin, a polypropylene resin, apolytetrafluoroethylene (PTFE) resin, an ABS resin, or cellulosenanofiber can be used, for example. Any of a variety of materials suchas glass, quartz, a resin, a metal, an alloy, and a semiconductor can beused for the substrate 351. The substrate 351 formed using any of avariety of materials such as glass, quartz, a resin, a metal, an alloy,and a semiconductor may be thin enough to be flexible.

Then, a separation starting point is formed in the first resin layer 23a, and the formation substrate 14 and the first resin layer 23 a areseparated from each other (FIG. 29A).

Next, the first resin layer 23 a and the second resin layer 23 b arepreferably removed. The first resin layer 23 a and the second resinlayer 23 b can be removed by a dry etching method, for example.Accordingly, the electrode 311 a is exposed (FIG. 29B).

In the case where the insulating film is positioned between the secondresin layer 23 b and the electrode 311 a, the insulating film may beeither removed or left. To remove the insulating film, a dry etchingmethod can be used, for example.

Subsequently, the alignment film 133 a is formed on the exposed surfaceof the electrode 311 a (or the insulating film) (FIG. 30A). Thealignment film 133 a can be formed in the following manner: a thin filmis formed using a resin or the like and then, rubbing treatment isperformed.

Then, the substrate 361 obtained from the steps described using FIG. 27Aand the substrate 351 obtained from the steps up to the step illustratedin FIG. 30A are bonded to each other with the liquid crystal layer 112provided therebetween (FIG. 30B). Although not illustrated in FIG. 30B,the substrate 351 and the substrate 361 are bonded to each other withthe bonding layer 141 as illustrated in FIG. 24 and other drawings. Formaterials for the bonding layer 141, the description of the materialsthat can be used for the bonding layer 142 can be referred to.

In the liquid crystal element 180 illustrated in FIG. 30B, the electrode311 a (and the electrode 311 b) part of which functions as the pixelelectrode, the liquid crystal layer 112, and the electrode 113 part ofwhich functions as the common electrode are stacked. The liquid crystalelement 180 is formed so as to overlap with the coloring layer 131.

The polarizing plate 135 is placed on the outer surface of the substrate361.

Through the above process, the display device 300 can be manufactured.

Manufacturing Method Example of Display Device 300B

Next, the manufacturing method of the display device of this embodimentwill be specifically described with reference to FIGS. 31A to 31D, FIGS.32A and 32B, and FIGS. 33A to 33C. An example of a manufacturing methodof the display device 300B illustrated in FIG. 26 will be describedbelow. Note that portions similar to those in the manufacturing methodexample of the display device 300 will not be described in some cases.

First, as in the manufacturing method example of the display device 300,the coloring layer 131, the insulating layer 121, the electrode 113, andthe alignment film 133 b are formed over the substrate 361 in that order(FIG. 31A).

Furthermore, the steps illustrated in FIG. 31B are performedindependently of the steps described with reference to FIG. 31A.

First, the transistor 80 is formed over the substrate 351. For thestructure and manufacturing method of the transistor 80, Embodiment 1can be referred to.

Then, the insulating layer 214, the insulating layer 216, thelight-emitting element 170, and the insulating layer 194 are formed(FIG. 31B). For the structures and formation methods of the insulatinglayer 214, the insulating layer 216, the light-emitting element 170, andthe insulating layer 194, the manufacturing method example of thedisplay device 300 can be referred to.

Furthermore, the steps illustrated in FIGS. 31C and 31D are performedindependently of the steps described with reference to FIG. 31A and thesteps described with reference to FIG. 31B.

First, the first resin layer 23 a having an island shape is formed overthe formation substrate 14 in a manner similar to that of themanufacturing method example 2 in Embodiment 1. Then, the second resinlayer 23 b is formed over the formation substrate 14 and the first resinlayer 23 a (FIG. 31C).

Specifically, the first layer 24 a is formed over the formationsubstrate 14, and a first heat treatment is performed on the first layer24 a having a desired shape, whereby the first resin layer 23 a isformed. The first heat treatment is performed in an atmospherecontaining oxygen. Then, the second layer 24 b is formed over theformation substrate 14 and the first resin layer 23 a, and a second heattreatment is performed on the second layer 24 b, whereby the secondresin layer 23 b is formed. The second heat treatment is performed in anatmosphere containing less oxygen than the atmosphere of the first heattreatment.

Next, the electrode 311 a is formed over the second resin layer 23 b,and the electrode 311 b is formed over the electrode 311 a (FIG. 31D).Each of the electrodes 311 a and 311 b can be formed in the followingmanner: a conductive film is formed, a resist mask is formed, theconductive film is etched, and the resist mask is removed. The electrode311 a is formed using a conductive material that transmits visiblelight. The electrode 311 b is formed using a conductive material thatreflects visible light.

The electrode 311 a may be formed over an insulating film formed overthe second resin layer 23 b. As the insulating film, an inorganicinsulating film that can be used to form the insulating layer 121 issuitably used. The insulating layer can be used as a barrier layer thatprevents diffusion of impurities contained in the first resin layer 23 aand the second resin layer 23 b into a transistor and a display elementformed later.

After that, the insulating layer 220 is formed (FIG. 31D). Then, anopening that reaches the electrode 311 b is formed in the insulatinglayer 220.

Then, the transistor 40 is formed over the insulating layer 220 (FIG.31D). For the structure and manufacturing method of the transistor 40,Embodiment 1 can be referred to.

After that, the insulating layer 212 that covers the transistor 40 isformed, the insulating layer 213 is formed over the insulating layer212, and the coloring layer 134 is formed over the insulating layer 213(FIG. 31D).

The substrate 351 obtained from the steps described with reference toFIG. 31B and the formation substrate 14 obtained from the steps up tothe steps illustrated in FIG. 31D, are bonded to each other using thebonding layer 142 (FIG. 32A).

Then, a separation starting point is formed in the first resin layer 23a, and the formation substrate 14 and the first resin layer 23 a areseparated from each other (FIG. 32B).

Next, the first resin layer 23 a and the second resin layer 23 b arepreferably removed. The first resin layer 23 a and the second resinlayer 23 b can be removed by a dry etching method, for example.Accordingly, the electrode 311 a is exposed (FIG. 33A).

In the case where the insulating film is positioned between the secondresin layer 23 b and the electrode 311 a, the insulating film may beeither removed or left. To remove the insulating film, a dry etchingmethod can be used, for example.

Subsequently, the alignment film 133 a is formed on the exposed surfaceof the electrode 311 a (or the insulating film) (FIG. 33B).

Then, the substrate 361 obtained from the step described using FIG. 31Aand the substrate 351 obtained from the steps up to the step illustratedin FIG. 33B are bonded to each other with the liquid crystal layer 112provided therebetween (FIG. 33C). Although not illustrated in FIG. 33C,the substrate 351 and the substrate 361 are bonded to each other with abonding layer.

In the liquid crystal element 180 illustrated in FIG. 33C, the electrode311 a (and the electrode 311 b) part of which functions as the pixelelectrode, the liquid crystal layer 112, and the electrode 113 part ofwhich functions as the common electrode are stacked. The liquid crystalelement 180 is formed so as to overlap with the coloring layer 131.

Through the above process, the display device 300B can be manufactured.

The display device of this embodiment includes two types of displayelements as described above; thus, switching between a plurality ofdisplay modes is possible. Accordingly, the display device can have highvisibility regardless of the ambient brightness, leading to highconvenience.

With the use of the method described in Embodiment 1, the first resinlayer 23 a can be separated from the formation substrate 14 withoutlaser irradiation performed on the entire area of the first resin layer23 a. Consequently, the display device can be manufactured at low costs.In addition, separation of the first resin layer 23 a from the formationsubstrate 14 at an unintended time can be avoided. Since the timing ofseparation can be controlled and high separability can be achieved, theyield of the separation process and the manufacturing process of adisplay device can be increased.

This embodiment can be combined with any of other embodiments asappropriate.

Embodiment 4

In this embodiment, more specific structure examples of the displaydevice described in Embodiment 3 will be described with reference toFIGS. 34A, 34B1, 34B2, 34B3, and 34B4, FIG. 35, and FIGS. 36A and 36B.

FIG. 34A is a block diagram of a display device 400. The display device400 includes the display portion 362, a circuit GD, and a circuit SD.The display portion 362 includes a plurality of pixels 410 arranged in amatrix.

The display device 400 includes a plurality of wirings G1, a pluralityof wirings G2, a plurality of wirings ANO, a plurality of wirings CSCOM,a plurality of wirings S1, and a plurality of wirings S2. The pluralityof wirings G1, the plurality of wirings G2, the plurality of wiringsANO, and the plurality of wirings CSCOM are each electrically connectedto the circuit GD and the plurality of pixels 410 arranged in adirection indicated by an arrow R. The plurality of wirings S1 and theplurality of wirings S2 are each electrically connected to the circuitSD and the plurality of pixels 410 arranged in a direction indicated byan arrow C.

Although the structure including one circuit GD and one circuit SD isillustrated here for simplicity, the circuit GD and the circuit SD fordriving liquid crystal elements and the circuit GD and the circuit SDfor driving light-emitting elements may be provided separately.

The pixels 410 each include a reflective liquid crystal element and alight-emitting element.

FIGS. 34B1, 34B2, 34B3, and 34B4 illustrate structure examples of theelectrode 311 included in the pixel 410. The electrode 311 serves as areflective electrode of the liquid crystal element. The opening 451 isprovided in the electrode 311 in FIGS. 34B1 and 34B2.

In FIGS. 34B1 and 34B2, a light-emitting element 360 positioned in aregion overlapping with the electrode 311 is indicated by a broken line.The light-emitting element 360 overlaps with the opening 451 included inthe electrode 311. Thus, light from the light-emitting element 360 isemitted to the display surface side through the opening 451.

In FIG. 34B1, the pixels 410 which are adjacent in the directionindicated by the arrow R are pixels emitting light of different colors.As illustrated in FIG. 34B1, the openings 451 are preferably provided indifferent positions in the electrodes 311 so as not to be aligned in twoadjacent pixels provided in the direction indicated by the arrow R. Thisallows two light-emitting elements 360 to be apart from each other,thereby preventing light emitted from the light-emitting element 360from entering a coloring layer in the adjacent pixel 410 (such aphenomenon is referred to as crosstalk). Furthermore, since two adjacentlight-emitting elements 360 can be arranged apart from each other, ahigh-resolution display device is achieved even when EL layers of thelight-emitting elements 360 are separately formed with a blocking maskor the like.

In FIG. 34B2, the pixels 410 which are adjacent in a direction indicatedby the arrow C are pixels emitting light of different colors. Also inFIG. 34B2, the openings 451 are preferably provided in differentpositions in the electrodes 311 so as not to be aligned in two adjacentpixels provided in the direction indicated by the arrow C.

The lower the ratio of the total area of the opening 451 to the totalarea except for the opening is, the brighter an image displayed usingthe liquid crystal element can be. Furthermore, the higher the ratio ofthe total area of the opening 451 to the total area except for theopening is, the brighter an image displayed using the light-emittingelement 360 can be.

The opening 451 may have a polygonal shape, a quadrangular shape, anelliptical shape, a circular shape, a cross-like shape, a stripe shape,a slit-like shape, or a checkered pattern, for example. The opening 451may be provided close to the adjacent pixel. Preferably, the opening 451is provided close to another pixel emitting light of the same color, inwhich case crosstalk can be suppressed.

As illustrated in FIGS. 34B3 and 34B4, a light-emitting region of thelight-emitting element 360 may be positioned in a region where theelectrode 311 is not provided, in which case light emitted from thelight-emitting element 360 is emitted to the display surface side.

In FIG. 34B3, the light-emitting elements 360 are not aligned in twoadjacent pixels 410 provided in the direction indicated by the arrow R.In FIG. 34B4, the light-emitting elements 360 are aligned in twoadjacent pixels 410 provided in the direction indicated by the arrow R.

The structure illustrated in FIG. 34B3 can, as mentioned above, preventcrosstalk and increase the resolution because the light-emittingelements 360 included in two adjacent pixels 410 can be apart from eachother. The structure illustrated in FIG. 34B4 can prevent light emittedfrom the light-emitting element 360 from being blocked by the electrode311 because the electrode 311 is not positioned along a side of thelight-emitting element 360 which is parallel to the direction indicatedby the arrow C. Thus, high viewing angle characteristics can beachieved.

As the circuit GD, any of a variety of sequential circuits such as ashift register can be used. In the circuit GD, a transistor, acapacitor, and the like can be used. A transistor included in thecircuit GD can be formed in the same steps as the transistors includedin the pixels 410.

The circuit SD is electrically connected to the wirings S1. For example,an integrated circuit can be used as the circuit SD. Specifically, anintegrated circuit formed on a silicon substrate can be used as thecircuit SD.

For example, a COG method, a COF method, or the like can be used tomount the circuit SD on a pad electrically connected to the pixels 410.Specifically, an anisotropic conductive film can be used to mount anintegrated circuit on the pad.

FIG. 35 is an example of a circuit diagram of the pixels 410. FIG. 35illustrates two adjacent pixels 410.

The pixels 410 each include a switch SW1, a capacitor C1, a liquidcrystal element 340, a switch SW2, a transistor M, a capacitor C2, thelight-emitting element 360, and the like. The pixel 410 is electricallyconnected to the wiring G1, the wiring G2, the wiring ANO, the wiringCSCOM, the wiring S1, and the wiring S2. FIG. 35 illustrates a wiringVCOM1 electrically connected to the liquid crystal element 340 and awiring VCOM2 electrically connected to the light-emitting element 360.

FIG. 35 illustrates an example in which a transistor is used as each ofthe switches SW1 and SW2.

A gate of the switch SW1 is connected to the wiring G1. One of a sourceand a drain of the switch SW1 is connected to the wiring S1, and theother is connected to one electrode of the capacitor C1 and oneelectrode of the liquid crystal element 340. The other electrode of thecapacitor C1 is connected to the wiring CSCOM. The other electrode ofthe liquid crystal element 340 is connected to the wiring VCOM1.

A gate of the switch SW2 is connected to the wiring G2. One of a sourceand a drain of the switch SW2 is connected to the wiring S2, and theother is connected to one electrode of the capacitor C2 and gates of thetransistor M. The other electrode of the capacitor C2 is connected toone of a source and a drain of the transistor M and the wiring ANO. Theother of the source and the drain of the transistor M is connected toone electrode of the light-emitting element 360. Furthermore, the otherelectrode of the light-emitting element 360 is connected to the wiringVCOM2.

FIG. 35 illustrates an example where the transistor M includes two gatesbetween which a semiconductor is provided and which are connected toeach other. This structure can increase the amount of current flowingthrough the transistor M.

The wiring G1 can be supplied with a signal for changing the on/offstate of the switch SW1. A predetermined potential can be supplied tothe wiring VCOM1. The wiring S1 can be supplied with a signal forchanging the orientation of liquid crystals of the liquid crystalelement 340. A predetermined potential can be supplied to the wiringCSCOM.

The wiring G2 can be supplied with a signal for changing the on/offstate of the switch SW2. The wiring VCOM2 and the wiring ANO can besupplied with potentials having a difference large enough to make thelight-emitting element 360 emit light. The wiring S2 can be suppliedwith a signal for changing the conduction state of the transistor M.

In the pixel 410 of FIG. 35, for example, an image can be displayed inthe reflective mode by driving the pixel with the signals supplied tothe wiring G1 and the wiring S1 and utilizing the optical modulation ofthe liquid crystal element 340. In the case where an image is displayedin the transmissive mode, the pixel is driven with the signals suppliedto the wiring G2 and the wiring S2 and the light-emitting element 360emits light. In the case where both modes are performed at the sametime, the pixel can be driven with the signals supplied to the wiringG1, the wiring G2, the wiring S1, and the wiring S2.

Although FIG. 35 illustrates an example in which one liquid crystalelement 340 and one light-emitting element 360 are provided in one pixel410, one embodiment of the present invention is not limited thereto.FIG. 36A illustrates an example in which one liquid crystal element 340and four light-emitting elements 360 (light-emitting elements 360 r, 360g, 360 b, and 360 w) are provided in one pixel 410. The pixel 410illustrated in FIG. 36A differs from that in FIG. 35 in being capable ofdisplaying a full-color image with the use of the light-emittingelements by one pixel.

In FIG. 36A, in addition to the wirings in FIG. 35, a wiring G3 and awiring S3 are connected to the pixel 410.

In the example in FIG. 36A, light-emitting elements emitting red light(R), green light (G), blue light (B), and white light (W) can be used asthe four light-emitting elements 360, for example. Furthermore, as theliquid crystal element 340, a reflective liquid crystal element emittingwhite light can be used. Thus, in the case of displaying an image in thereflective mode, a white image can be displayed with high reflectivity.In the case of displaying an image in the transmissive mode, an imagecan be displayed with a higher color rendering property at low powerconsumption.

FIG. 36B illustrates a structure example of the pixel 410 correspondingto FIG. 36A. The pixel 410 includes the light-emitting element 360 woverlapping with the opening included in the electrode 311 and thelight-emitting element 360 r, the light-emitting element 360 g, and thelight-emitting element 360 b which are arranged in the periphery of theelectrode 311. It is preferable that the light-emitting elements 360 r,360 g, and 360 b have almost the same light-emitting area.

This embodiment can be combined with any other embodiment asappropriate.

Embodiment 5

In this embodiment, a display module and electronic devices ofembodiments of the present invention are described.

In a display module 8000 in FIG. 37, a touch panel 8004 connected to anFPC 8003, a display panel 8006 connected to an FPC 8005, a frame 8009, aprinted circuit board 8010, and a battery 8011 are provided between anupper cover 8001 and a lower cover 8002.

The display device fabricated using the separation method of oneembodiment of the present invention can be used for, for example, thedisplay panel 8006. Thus, the display module can be manufactured withhigh yield.

The shapes and sizes of the upper cover 8001 and the lower cover 8002can be changed as appropriate in accordance with the sizes of the touchpanel 8004 and the display panel 8006.

The touch panel 8004 can be a resistive touch panel or a capacitivetouch panel and can be formed to overlap with the display panel 8006.Instead of providing the touch panel 8004, the display panel 8006 mayhave a touch panel function.

The frame 8009 protects the display panel 8006 and functions as anelectromagnetic shield for blocking electromagnetic waves generated bythe operation of the printed circuit board 8010. The frame 8009 can alsofunction as a radiator plate.

The printed circuit board 8010 includes a power supply circuit and asignal processing circuit for outputting a video signal and a clocksignal. As a power source for supplying power to the power supplycircuit, an external commercial power source or the battery 8011provided separately may be used. The battery 8011 can be omitted in thecase of using a commercial power source.

The display module 8000 may be additionally provided with a member suchas a polarizing plate, a retardation plate, or a prism sheet.

According to one embodiment of the present invention, highly reliableelectronic devices having curved surfaces can be manufactured. Accordingto one embodiment of the present invention, flexible and highly reliableelectronic devices can be manufactured.

Examples of the electronic devices include a television set, a desktopor laptop personal computer, a monitor of a computer or the like, adigital camera, a digital video camera, a digital photo frame, a mobilephone, a portable game machine, a portable information terminal, anaudio reproducing device, and a large game machine such as a pachinkomachine.

The display device of one embodiment of the present invention canachieve high visibility regardless of the intensity of external light.Thus, the display device of one embodiment of the present invention canbe suitably used for a portable electronic device, a wearable electronicdevice (wearable device), an e-book reader, or the like.

A portable information terminal 800 illustrated in FIGS. 38A and 38Bincludes a housing 801, a housing 802, a display portion 803, a displayportion 804, a hinge portion 805, and the like.

The housing 801 and the housing 802 are joined together with the hingeportion 805. The portable information terminal 800 can be opened asillustrated in FIG. 38B from a closed state (FIG. 38A).

The display device manufactured using the separation method of oneembodiment of the present invention can be used for at least one of thedisplay portion 803 and the display portion 804. Thus, the portableinformation terminal can be manufactured with high yield.

The display portion 803 and the display portion 804 can each display atleast one of a text, a still image, a moving image, and the like. When atext is displayed on the display portion, the portable informationterminal 800 can be used as an e-book reader.

Since the portable information terminal 800 is foldable, the portableinformation terminal 800 has high portability and excellent versatility.

A power button, an operation button, an external connection port, aspeaker, a microphone, or the like may be provided for the housing 801and the housing 802.

A portable information terminal 810 illustrated in FIG. 38C includes ahousing 811, a display portion 812, an operation button 813, an externalconnection port 814, a speaker 815, a microphone 816, a camera 817, andthe like.

The display device manufactured using the separation method of oneembodiment of the present invention can be used for the display portion812. Thus, the portable information terminal can be manufactured withhigh yield.

The portable information terminal 810 includes a touch sensor in thedisplay portion 812. Operations such as making a call and inputting acharacter can be performed by touch on the display portion 812 with afinger, a stylus, or the like.

With the operation button 813, the power can be turned on or off. Inaddition, types of images displayed on the display portion 812 can beswitched; for example, switching an image from a mail creation screen toa main menu screen is performed with the operation button 813.

When a detection device such as a gyroscope sensor or an accelerationsensor is provided inside the portable information terminal 810, thedirection of display on the screen of the display portion 812 can beautomatically changed by determining the orientation of the portableinformation terminal 810 (whether the portable information terminal 810is placed horizontally or vertically). Furthermore, the direction ofdisplay on the screen can be changed by touch on the display portion812, operation with the operation button 813, sound input using themicrophone 816, or the like.

The portable information terminal 810 functions as, for example, one ormore of a telephone set, a notebook, and an information browsing system.Specifically, the portable information terminal 810 can be used as asmartphone. The portable information terminal 810 is capable ofexecuting a variety of applications such as mobile phone calls,e-mailing, viewing and editing texts, music reproduction, reproducing amoving image, Internet communication, and computer games, for example.

A camera 820 illustrated in FIG. 38D includes a housing 821, a displayportion 822, operation buttons 823, a shutter button 824, and the like.Furthermore, an attachable lens 826 is attached to the camera 820.

The display device manufactured using the separation method of oneembodiment of the present invention can be used for the display portion822. Thus, the camera can be manufactured with high yield.

Although the lens 826 of the camera 820 here is detachable from thehousing 821 for replacement, the lens 826 may be incorporated into thehousing 821.

A still image or a moving image can be taken with the camera 820 at thepress of the shutter button 824. In addition, images can also be takenby the touch of the display portion 822 which has a function of a touchpanel.

Note that a stroboscope, a viewfinder, or the like can be additionallyattached to the camera 820. Alternatively, these may be incorporatedinto the housing 821.

FIGS. 39A to 39E illustrate electronic devices. These electronic deviceseach include a housing 9000, a display portion 9001, a speaker 9003, anoperation key 9005 (including a power switch or an operation switch), aconnection terminal 9006, a sensor 9007 (a sensor having a function ofmeasuring force, displacement, position, speed, acceleration, angularvelocity, rotational frequency, distance, light, liquid, magnetism,temperature, chemical substance, sound, time, hardness, electric field,current, voltage, power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared rays), a microphone 9008, and the like.

The display device manufactured using the separation method of oneembodiment of the present invention can be favorably used for thedisplay portion 9001. Thus, the electronic devices can be manufacturedwith high yield.

The electronic devices illustrated in FIGS. 39A to 39E can have avariety of functions, for example, a function of displaying a variety ofinformation (a still image, a moving image, a text image, and the like)on the display portion, a touch panel function, a function of displayinga calendar, the date, the time, and the like, a function of controllingprocessing with a variety of software (programs), a wirelesscommunication function, a function of being connected to a variety ofcomputer networks with a wireless communication function, a function oftransmitting and receiving a variety of data with a wirelesscommunication function, a function of reading a program or data storedin a storage medium and displaying the program or data on the displayportion, and the like. Note that the functions of the electronic devicesillustrated in FIGS. 39A to 39E are not limited to the above, and theelectronic devices may have other functions.

FIG. 39A is a perspective view of a watch-type portable informationterminal 9200. FIG. 39B is a perspective view of a watch-type portableinformation terminal 9201.

The portable information terminal 9200 illustrated in FIG. 39A iscapable of executing a variety of applications such as mobile phonecalls, e-mailing, viewing and editing texts, music reproduction,Internet communication, and computer games. The display surface of thedisplay portion 9001 is bent, and an image can be displayed on the bentdisplay surface. The portable information terminal 9200 can employ nearfield communication conformable to a communication standard. In thatcase, for example, mutual communication between the portable informationterminal 9200 and a headset capable of wireless communication can beperformed, and thus hands-free calling is possible. The portableinformation terminal 9200 includes the connection terminal 9006, anddata can be directly transmitted to and received from anotherinformation terminal via a connector. Power charging through theconnection terminal 9006 is also possible. Note that the chargingoperation may be performed by wireless power feeding without using theconnection terminal 9006.

Unlike in the portable information terminal illustrated in FIG. 39A, thedisplay surface of the display portion 9001 is not curved in theportable information terminal 9201 illustrated in FIG. 39B. Furthermore,the external state of the display portion of the portable informationterminal 9201 is a non-rectangular shape (a circular shape in FIG. 39B).

FIGS. 39C to 39E are perspective views of a foldable portableinformation terminal 9202. FIG. 39C is a perspective view illustratingthe portable information terminal 9202 that is opened. FIG. 39D is aperspective view illustrating the portable information terminal 9202that is being opened or being folded. FIG. 39E is a perspective viewillustrating the portable information terminal 9202 that is folded.

The folded portable information terminal 9202 is highly portable, andthe opened portable information terminal 9202 is highly browsable due toa seamless large display region. The display portion 9001 of theportable information terminal 9202 is supported by three housings 9000joined together by hinges 9055. By folding the portable informationterminal 9202 at a connection portion between two housings 9000 with thehinges 9055, the portable information terminal 9202 can be reversiblychanged in shape from opened to folded. For example, the portableinformation terminal 9202 can be bent with a radius of curvature ofgreater than or equal to 1 mm and less than or equal to 150 mm.

This embodiment can be combined with any other embodiment asappropriate.

Example 1

In this example, the effect that the baking conditions used to form aresin layer over a formation substrate have on the separability of theresin layer was evaluated.

<1. Baking Atmosphere>

First, two samples fabricated in different baking atmospheres forforming a resin layer were compared.

As a formation substrate of each sample, an approximately 0.7-mm-thickglass substrate was used. As a resin layer, a polyimide resin film wasformed over the formation substrate of each sample. The polyimide resinfilm was formed using a photosensitive material including a polyimideresin precursor. The thickness of the polyimide resin film atapplication of the material was approximately 2.0 μm. The thickness ofthe polyimide resin film after being subjected to baking wasapproximately 1.5 μm.

A sample 1A was subjected to baking at 450° C. for one hour whilesupplying a mixed gas of a nitrogen gas and an oxygen gas (oxygenconcentration of 20%) with a flow rate of 580 NL/min.

A sample 1B was subjected to baking at 450° C. for one hour whilesupplying a nitrogen gas with a flow rate of 600 NL/min. The oxygenconcentration in the apparatus during the baking was approximately 0.01%to 0.02%.

Then, a UV separation tape was attached to each of the resin layers andwas pulled by a hand to be separated from the formation substrate.

FIG. 40A shows the results of separation of the sample 1A. FIG. 40Bshows separation results of the sample 1B. In each of the photographs,the portion above a solid line is the tape side and the portion belowthe solid line is the glass side.

As shown in FIG. 40A, in the sample 1A, the resin layer 23 remained onthe tape side, which allowed separation to occur at an interface betweenthe formation substrate 14 and the resin layer 23.

As shown in FIG. 40B, in the sample 1B, the resin layer 23 remained onthe formation substrate 14 side after separation, which did not allowseparation to occur at the interface between the formation substrate 14and the resin layer 23.

The sample 1A and the sample 1B are different from each other in abaking atmosphere for forming the resin layer 23. Thus, it is consideredthat the resin layer 23 can be easily separated from the formationsubstrate 14 when the resin layer 23 is formed through baking in anatmosphere containing a sufficient amount of oxygen. It is consideredthat unintentional separation of the resin layer 23 from the formationsubstrate 14 can be avoided by forming the resin layer 23 through bakingin an atmosphere containing small amount of oxygen.

<2. Baking Temperature and Thickness of Resin Layer>

Next, nine samples were compared. Resin layers of the nine samples wereformed at different baking temperatures and have different thicknesses.

As the formation substrate of each sample, an approximately 0.7-mm-thickglass substrate was used. As the resin layer, a polyimide resin film wasformed over the formation substrate of each sample. The polyimide resinfilm was formed using a photosensitive material including a polyimideresin precursor. After the material was applied, the resin layer wasformed through baking for one hour while supplying a mixed gas ofnitrogen gas and oxygen gas (oxygen concentration of 20%) with a flowrate of 580 NL/min.

Table 1 shows baking temperatures and the thicknesses of the resinlayers at application of the material of each of the samples. Forexample, in Table 1, the thickness of 2.0 μm means that the material ofthe resin layer (the material containing a polyimide resin precursor)was applied to have a thickness of 2.0 μm. Note that the thickness ofthe resin layer after baking was less than 2.0 μm.

TABLE 1 Baking temperature of resin layer 350° C. 400° C. 450° C.Thickness of resin 2.0 μm Sample 1C Sample 1D Sample 1E layer 1.0 μmSample 1F Sample 1G Sample 1H (at application) 0.2 μm Sample 1I Sample1J Sample 1K

Next, the resin layer and a film were attached to each other with anadhesive layer.

As the adhesive layer, an approximately 5-μm-thick thermosetting epoxyresin was used. The film has a stacked-layer structure including anapproximately 23-μm-thick film and an approximately 100-μm-thickprotective film.

Next, a cutter was inserted from the film side into a portion locatedinward from an end portion of the resin layer to make a cut in aframe-like shape. Then, the film was pulled by a hand to be separatedfrom the formation substrate.

Table 2 shows the results of separation of the samples. The samples inwhich separation occurred at the interface between the formationsubstrate and the resin layer are indicated by circles. The samples inwhich separation did not occur at the interface between the formationsubstrate and the resin layer are indicated by crosses.

TABLE 2 Baking temperature of resin layer 350° C. 400° C. 450° C.Thickness of resin 2.0 μm x x ∘ layer 1.0 μm x x ∘ (at application) 0.2μm x x ∘

FIG. 41 shows results of separation of the sample 1E (the thickness ofthe resin layer at application was 2.0 μm, and the baking temperaturewas 450° C.). In the portion inside the frame-like cut made by thecutter, the resin layer 23 was able to be separated from the formationsubstrate 14.

In this example, in any of the samples subjected to baking at 450° C.,the resin layer was able to be separated from the formation substrateregardless of the thickness of the resin layer. In any of the samplessubjected to baking at 350° C. or 400° C., the resin layer was not ableto be separated from the formation substrate regardless of the thicknessof the resin layer.

The above results indicate that baking performed in an atmospherecontaining a sufficient amount of oxygen at a high temperature enablesthe resin layer to be easily separated from the formation substrateregardless of the thickness of the resin layer. The results alsoindicate that, even in an atmosphere containing a sufficient amount ofoxygen, forming the resin layer through baking at a low temperaturesuppresses unintentional separation of the resin layer from theformation substrate.

Example 2

In this example, results of separating a resin layer from a formationsubstrate by a separation method of one embodiment of the presentinvention will be described.

First, as shown in FIGS. 42A1 and 42A2, the island-shaped first resinlayer 23 a was formed over the formation substrate 14 by aphotolithography method. Next, the second resin layer 23 b was formedover the formation substrate 14 and the first resin layer 23 a. Thesecond resin layer 23 b was formed to cover the first resin layer 23 a.The formation substrate 14 includes a portion which is in contact withthe first resin layer 23 a and a portion which is in contact with thesecond resin layer 23 b.

As the formation substrate 14, an approximately 0.7 mm thick5-inch-square glass substrate was used.

A photosensitive material containing a polyimide resin precursor wasapplied, processed into an island shape, and subjected to baking at 450°C. for one hour while supplying a mixed gas of a nitrogen gas and anoxygen gas (oxygen concentration of 20%) with a flow rate of 580 NL/min,whereby the first resin layer 23 a was formed. The thickness of theresin layer at application of the material was different between samples(see Table 3).

The photosensitive material containing a polyimide resin precursor wasapplied and subjected to baking at 450° C. for one hour in a mixedatmosphere of nitrogen and oxygen, whereby the second resin layer 23 bwas formed. The thickness of the layer to be a resin layer atapplication of the material was different between samples (see Table 3).

TABLE 3 Thickness of the first resin layer 23a (at application) 2.0 μm1.0 μm 0.2 μm Thickness of the 2.0 μm Sample 2A Sample 2C Sample 2Esecond resin layer 23b 1.0 μm Sample 2B Sample 2D Sample 2F (atapplication)

Next, the second resin layer 23 b and the film 27 were attached to eachother using an adhesive layer 26 (see FIG. 42B).

As the adhesive layer, an approximately 5-μm-thick thermosetting epoxyresin was used. The film has a stacked-layer structure including anapproximately 23-μm-thick film and an approximately 100-μm-thickprotective film.

Next, an instrument 65 (here, a cutter) was inserted from the film 27side into a portion located inward from an end portion of the firstresin layer 23 a to make a cut 64 in a frame-like shape (FIGS. 42C1 and42C2). Then, the film 27 was pulled by a hand to be separated from theformation substrate 14 (FIG. 42D).

FIG. 43 shows external photographs each showing the sample afterseparation. In a portion of the resin layer 23 inside the cut 64, theresin layer 23 was able to be separated from the formation substrate 14without the remaining film.

[Separation Test]

The force required to separate the layer to be separated from theformation substrate 14 was measured in each of the samples of Example 1.A jig illustrated in FIG. 44A was used for the measurement. The jigillustrated in FIG. 44A includes a plurality of guide rollers 154 and asupport roller 153. First, a tape 151 is attached onto a layer 150 to beseparated that has been formed over the formation substrate 14, and anend portion of the tape 151 is partly separated in advance. Then, theformation substrate 14 is fixed to the jig so that the tape 151 is heldby the support roller 153, and the tape 151 and the layer 150 to beseparated are positioned perpendicular to the formation substrate 14.The force required for separating was measured as follows: the tape 151was pulled at a rate of 20 mm/min in a direction perpendicular to theformation substrate 14 to separate the layer 150 to be separated fromthe formation substrate 14, and the pulling force in the perpendiculardirection was measured. During the separation, the formation substrate14 moves in the plane direction along the guide rollers 154 with thefirst resin layer 23 a exposed. The support roller 153 and the guiderollers 154 are rotatable so that the formation substrate 14 and thelayer 150 to be separated are not affected by friction during the move.

For the separation test, a compact table-top universal tester (EZ-TESTEZ-S-50N) manufactured by Shimadzu Corporation was used, and an adhesivetape/adhesive sheet testing method based on standard number JIS Z0237 ofJapanese Industrial Standards (JIS) was employed. Each sample had a sizeof 126 mm×25 mm.

FIG. 44B shows the stacked-layer structure of the layer 150 to beseparated.

The layer 150 to be separated includes the first resin layer 23 a overthe formation substrate 14, the second resin layer 23 b over the firstresin layer 23 a, the adhesive layer 26 over the second resin layer 23b, and the film 27 over the adhesive layer 26. The thicknesses of thefirst resin layer 23 a and the second resin layer 23 b at applicationare different between samples, and the details are shown in Table 3.

FIG. 45 shows results of the separation test. As shown in FIG. 45, thelarger the thickness of the first resin layer 23 a is, the smaller theforce required for separation tends to be. The force required forseparation does not change even when the thickness of the second resinlayer 23 b is changed.

FIGS. 46A to 46C, FIGS. 47A to 47C, and FIGS. 48A to 48C showcross-sectional STEM images of a sample 2A, a sample 2C, and a sample 2Ebefore and after separation, respectively.

FIG. 46A, FIG. 47A, and FIG. 48A show cross sectional STEM images of thesample 2A, the sample 2C, and the sample 2E, respectively. The imagesshow the samples before separation.

As shown in FIG. 46A, in the sample 2A, the thickness of thestacked-layer structure including the first resin layer 23 a and thesecond resin layer 23 b is approximately 2.58 μm.

As shown in FIG. 47A, in the sample 2C, the thickness of thestacked-layer structure including the first resin layer 23 a and thesecond resin layer 23 b is approximately 1.82 μm.

As shown in FIG. 48A, in the sample 2E, the thickness of thestacked-layer structure including the first resin layer 23 a and thesecond resin layer 23 b is approximately 1.40 μm.

FIG. 46B, FIG. 47B, and FIG. 48B show cross-sectional STEM images of thesample 2A, the sample 2C, and the sample 2E, respectively, on theformation substrate 14 side. The images show samples after separation.

In each of the samples, the resin layer was not observed on a glasssurface after separation.

FIG. 46C, FIG. 47C, and FIG. 48C show cross-sectional STEM images of thesample 2A, the sample 2C, and the sample 2E, respectively, on the film27 side. The images show samples after separation.

As shown in FIG. 46C, it is found that in the sample 2A, a stacked-layerstructure with a thickness of approximately 2.50 μm including the firstresin layer 23 a and the second resin layer 23 b is on the film 27 side.

As shown in FIG. 47C, it is found that in the sample 2C, a stacked-layerstructure with a thickness of approximately 1.85 μm including the firstresin layer 23 a and the second resin layer 23 b is on the film 27 side.

As shown in FIG. 48C, it is found that in the sample 2E, a stacked-layerstructure with a thickness of approximately 1.40 μm including the firstresin layer 23 a and the second resin layer 23 b is on the film 27 side.

According to the results of a cross-sectional observation, it was shownthat separation was performed at the interface between the formationsubstrate 14 and the first resin layer 23 a.

Example 3

In this example, the effect that the baking conditions used to form aresin layer over a formation substrate have on the separability of theresin layer was evaluated. In this example, results of forming the resinlayer using a material different from the material in Example 1 will bedescribed.

As a formation substrate of each sample, an approximately 0.7-mm-thickglass substrate was used. As a resin layer, a polyimide resin film wasformed over the formation substrate of each sample. The polyimide resinfilm was formed by a spin coating method. The polyimide resin film wasformed under the following conditions: the temperature was roomtemperature, the application amount was 40 ml, and the application timewas 12.5 sec. The number of revolutions at application in the sample 3Awas 500 rpm. The numbers of revolutions at application in the samples 3Band 3C were each 1000 rpm. The deposition conditions were determined sothat the resin layers of the three samples have approximately the samethickness after baking. The polyimide resin film was formed using anon-photosensitive material including a soluble polyimide resin.

For Sample 3A, baking was performed at 180° C. for 30 minutes while amixed gas of a nitrogen gas and an oxygen gas (580 NL/min, oxygenconcentration: 20%) was supplied, and then, baking was performed at 450°C. for 1 hour while the same mixed gas was supplied. The thickness ofthe resin layer after the baking was approximately 1.11 μm.

For Sample 3B, baking was performed at 180° C. for 30 minutes while amixed gas of a nitrogen gas and an oxygen gas (580 NL/min, oxygenconcentration: 20%) was supplied, and then, baking was performed at 400°C. for 1 hour while the same mixed gas was supplied. The thickness ofthe resin layer after the baking was approximately 1.01 μm.

For Sample 3C, baking was performed at 180° C. for 30 minutes while amixed gas of a nitrogen gas and an oxygen gas (580 NL/min, oxygenconcentration: 20%) was supplied, and then, baking was performed at 350°C. for 1 hour while the same mixed gas was supplied. The thickness ofthe resin layer after the baking was approximately 1.07 μm.

In each of the samples 3A, 3B, and 3C, when a separation test wasperformed in a manner similar to that in Example 2, separation was ableto be made at the interface between the formation substrate and theresin layer.

The force required for separation in Sample 3A was 0.091 N. The forcerequired for separation in Sample 3B was 0.169 N. There is no largedifference between the thicknesses of Sample 3A and Sample 3B; thus, itcan be presumed that the force required for separation in Sample A isreduced by baking at a higher temperature.

In this example, a resin layer was formed using non-photosensitivematerial. In contrast, in Example 1, the resin layer was formed using aphotosensitive material. It is revealed from the results of the examplethat, when the resin layer is formed through baking at a hightemperature in an atmosphere containing sufficient oxygen, the resinlayer can be separated from the formation substrate regardless of thephotosensitivity of the material for the resin layer.

In Example 1, only in the samples subjected to baking at 450° C.,separation was able to be made at the interface between the formationsubstrate and the resin layer. In the sample subjected to baking at 350°C. or 400° C., separation was not able to be made at the interface.

On the other hand, in this example, without being limited to the samplesubjected to baking at 450° C., separation was able to be made at theinterface between the formation substrate and the resin layer even inthe material subjected to 350° C. or 400° C. This suggests that afavorable range of the baking temperature is different depending onmaterials used for the resin layer.

The above results show that, by forming the resin layer through bakingat a high temperature in an atmosphere containing enough oxygen, theresin layer can be separated from the formation substrate.

Example 4

In this example, the XPS analysis results of a surface on the formationsubstrate side of a resin layer formed over a formation substrate aredescribed.

The surface on the formation substrate side of the resin layercorresponds to a surface exposed by the separation process.

In this example, six samples (samples 4A to 4F) and a comparative samplewere fabricated.

In the samples 4A to 4F, separation can be made at the interface betweenthe formation substrate and the resin layer even when a particulartreatment is not performed (e.g., a treatment of irradiating the entiresurface of the resin layer with laser light). In the comparative sample,separation cannot be made at the interface between the formationsubstrate and the resin layer when the particular treatment is notperformed.

As the formation substrate of each sample, an approximately 0.7-mm-thickglass substrate was used.

As the resin layer, a polyimide resin film was formed over the formationsubstrate of each sample. The polyimide resin films were formed by aspin coating method.

In each of the samples 4A, 4B, and 4C, and the comparative sample, thepolyimide resin film was formed using a photosensitive materialincluding a polyimide resin precursor. The polyimide resin film wasformed to have a thickness of approximately 2.0 μm when the material wasapplied.

The sample 4A, the sample 4B, and the sample 4C were subjected to bakingat 450° C. while supplying a mixed gas of a nitrogen gas and an oxygengas (oxygen concentration of 20%) with a flow rate of 580 NL/min. Thetime for baking performed on the sample 4A, the sample 4B, and thesample 4C were 1 hour, 2 hours, and 3 hours, respectively.

The comparative sample was subjected to baking at 450° C. for one hourwhile supplying a nitrogen gas with a flow rate of 600 NL/min. Theoxygen concentration in the apparatus during the baking wasapproximately 0.01% to 0.02%.

The deposition conditions of the samples 4D, 4E, and 4F were determinedso that the resin layers of the three samples after baking haveapproximately the same thickness. Specifically, the polyimide resinfilms were formed under the following conditions: the temperature wasroom temperature, the application quantity was 40 ml, and theapplication time was 12.5 sec. The numbers of revolutions at theapplication in the samples 4D and 4E were each 1000 rpm. The number ofrevolutions at the application in the sample 4F was 500 rpm. Thepolyimide resin film was formed using a non-photosensitive materialincluding a soluble polyimide resin.

For the sample 4D, the sample 4E, and the sample 4F, baking wasperformed at 180° C. for 30 minutes while a mixed gas of a nitrogen gasand an oxygen gas (580 NL/min, oxygen concentration: 20%) was supplied,and then, baking was performed for 1 hour while the same mixed gas wassupplied. The temperature of the 1-hour baking was 350° C. for Sample4D, 400° C. for Sample 4E, and 450° C. for Sample 4F.

In each sample, XPS analysis was performed on the surface on theformation substrate side.

FIGS. 49A and 49B show oxygen concentration of each of the samples.

Oxygen concentration of the comparative sample was approximately 6.8atomic %. The oxygen concentration of the samples 4A to 4F each exceeded15 atomic %. Each of the oxygen concentration of the samples 4A to 4Fwas higher than the oxygen concentration of the comparative sample.

The sample 4D to the sample 4F were formed such that the resin layers inthe samples after being baked had almost the same film thickness. Theforces required for separation in samples having the same structures asthe sample 4D to sample 4F were evaluated. The evaluation shows that thestructure of the sample 4D required the largest force for separation andthe structure of the sample 4F required the smallest force forseparation. According to this and the results shown in FIG. 49B, thereis a tendency that the higher the oxygen concentration is, the smallerthe force required for separation is. This suggests that the oxygenconcentration measured by the XPS analysis performed on the surface onthe separation surface side of the resin layer is preferably high.

REFERENCE NUMERALS

10A: display device, 10B: display device, 13: adhesive layer, 14:formation substrate, 22: substrate, 23: resin layer, 23 a: first resinlayer, 23 b: second resin layer, 24 a: first layer, 24 b: second layer,26: adhesive layer, 27: film, 28: adhesive layer, 29: substrate, 31:insulating layer, 32: insulating layer, 33: insulating layer, 34:insulating layer, 35: insulating layer, 40: transistor, 41: conductivelayer, 43 a: conductive layer, 43 b: conductive layer, 43 c: conductivelayer, 44: metal oxide layer, 45: conductive layer, 49: transistor, 60:light-emitting element, 61: conductive layer, 62: EL layer, 63:conductive layer, 64: cut, 65: instrument, 66: laser light, 67:irradiation region, 71: protective layer, 74: insulating layer, 75:protective layer, 75 a: substrate, 75 b: adhesive layer, 76: connector,80: transistor, 81: conductive layer, 82: insulating layer, 83: metaloxide layer, 83 a: channel region, 83 b: LDD region, 83 c:low-resistance region, 84: insulating layer, 85: conductive layer, 86 a:conductive layer, 86 b: conductive layer, 86 c: conductive layer, 90:transistor, 91: formation substrate, 93 a: first resin layer, 93 b:second resin layer, 95: insulating layer, 97: coloring layer, 98:light-blocking layer, 98 a: partition, 98 b: partition, 99: adhesivelayer, 112: liquid crystal layer, 113: electrode, 117: insulating layer,121: insulating layer, 131: coloring layer, 132: light-blocking layer,133 a: alignment film, 133 b: alignment film, 134: coloring layer, 135:polarizing plate, 141: adhesive layer, 142: adhesive layer, 150: layerto be separated, 151: tape, 153: support roller, 154: guide roller, 170:light-emitting element, 180: liquid crystal element, 191: electrode,192: EL layer, 193: electrode, 194: insulating layer, 201: transistor,203: transistor, 204: connection portion, 205: transistor, 206:transistor, 207: connection portion, 211: insulating layer, 212:insulating layer, 213: insulating layer, 214: insulating layer, 216:insulating layer, 217: insulating layer, 220: insulating layer, 221 a:conductive layer, 221 b: conductive layer, 222 a: conductive layer, 222b: conductive layer, 223: conductive layer, 231: semiconductor layer,242: connection layer, 243: connector, 252: connection portion, 261:semiconductor layer, 263 a: conductive layer, 263 b: conductive layer,281: transistor, 284: transistor, 285: transistor, 286: transistor, 300:display device, 300A: display device, 300B: display device, 311:electrode, 311 a: electrode, 311 b: electrode, 340: liquid crystalelement, 351: substrate, 360: light-emitting element, 360 b:light-emitting element, 360 g: light-emitting element, 360 r:light-emitting element, 360 w: light-emitting element, 361: substrate,362: display portion, 364: circuit, 365: wiring, 372: FPC, 373: IC, 381:display portion, 382: driver circuit portion, 400: display device, 410:pixel, 451: opening, 800: portable information terminal, 801: housing,802: housing, 803: display portion, 804: display portion, 805: hingeportion, 810: portable information terminal, 811: housing, 812: displayportion, 813: operation button, 814: external connection port, 815:speaker, 816: microphone, 817: camera, 820: camera, 821: housing, 822:display portion, 823: operation button, 824: shutter button, 826: lens,8000: display module, 8001: upper cover, 8002: lower cover, 8003: FPC,8004: touch panel, 8005: FPC, 8006: display panel, 8009: frame, 8010:printed circuit board, 8011: battery, 9000: housing, 9001: displayportion, 9003: speaker, 9005: operation key, 9006: connection terminal,9007: sensor, 9008: microphone, 9055: hinge, 9200: portable informationterminal, 9201: portable information terminal, and 9202: portableinformation terminal.

This application is based on Japanese Patent Application serial no.2016-149840 filed with Japan Patent Office on Jul. 29, 2016, the entirecontents of which are hereby incorporated by reference.

1. A method for manufacturing a semiconductor device comprising thesteps of: forming a first layer comprising a resin over a substrate;performing a first heat treatment on the first layer in a firstatmosphere; forming a second layer to cover an end portion of the firstlayer and in contact with the substrate outside of the first layer afterperforming the first heat treatment; performing a second heat treatmentafter forming the second layer in a second atmosphere; and separatingthe second layer from the substrate, wherein the second atmosphere has alower oxygen concentration than the first atmosphere.
 2. The method formanufacturing a semiconductor device according to claim 1, wherein thesecond layer comprises a resin after performing the second heattreatment.
 3. The method for manufacturing a semiconductor deviceaccording to claim 1, further comprising the step of: forming atransistor over the second layer, wherein the transistor is separatedfrom the substrate by the separation step.
 4. The method formanufacturing a semiconductor device according to claim 1, wherein asurface of the second layer is exposed during the second heat treatment.5. The method for manufacturing a semiconductor device according toclaim 1, wherein a temperature of the second heat treatment is lowerthan a temperature of the first heat treatment.
 6. The method formanufacturing a semiconductor device according to claim 1, wherein theseparation is performed at an interface between the substrate and thefirst layer.
 7. The method for manufacturing a semiconductor deviceaccording to claim 1, wherein the first layer is formed by using aphotosensitive material.
 8. A method for manufacturing a semiconductordevice comprising the steps of: forming a first resin layer comprising aresin or a resin precursor over a substrate; performing a prebakingtreatment on the first resin layer to form a second resin layer;removing a part of the second resin layer to form a third resin layerafter performing the prebaking treatment; performing a first heattreatment on the third resin layer in a first atmosphere; forming aninsulating layer to cover an end portion of the third resin layer and incontact with the substrate; performing a second heat treatment on theinsulating layer in a second atmosphere; and separating the insulatinglayer from the substrate, wherein the second atmosphere has a loweroxygen concentration than the first atmosphere.
 9. The method formanufacturing a semiconductor device according to claim 8, wherein thefirst resin layer comprises a photosensitive material.
 10. The methodfor manufacturing a semiconductor device according to claim 8, whereinthe insulating layer is formed by using a photosensitive material. 11.The method for manufacturing a semiconductor device according to claim8, further comprising the step of: exposing the first resin layer tolight.
 12. The method for manufacturing a semiconductor device accordingto claim 8, wherein removing the part of the second resin layer isperformed by forming a resist mask and processing the part of the secondresin layer.
 13. The method for manufacturing a semiconductor deviceaccording to claim 8, wherein a surface of the insulating layer isexposed during the second heat treatment.
 14. The method formanufacturing a semiconductor device according to claim 8, furthercomprising the step of: forming a transistor over the insulating layer,wherein the transistor is separated from the substrate by the separationstep.
 15. The method for manufacturing a semiconductor device accordingto claim 8, wherein a temperature of the second heat treatment is lowerthan a temperature of the first heat treatment.
 16. The method formanufacturing a semiconductor device according to claim 8, wherein theseparation is performed at an interface between the substrate and thethird resin layer.